=head1	NAME

ODF::lpOD::TextElement - Basic text containers

=head1  DESCRIPTION

All the text content of a document belong to I<paragraphs>. Paragraphs may be
included in various structured containers (such as tables, sections, and
others) introduced in other manual pages. Some particular paragraphs have a
hierarchical level and are called I<headings>. A paragraph have a I<style>, but
some text segments in a paragraph, so-called I<text spans>, may have particular
styles. In addition, a paragraph may include special markup elements, namely
I<bookmarks>, I<index marks>, I<bibliography marks>, and I<notes>.

Paragraphs and headings are represented by C<odf_paragraph> and C<odf_heading>
objects in the lpOD library. C<odf_heading> is a subclass of C<odf_paragraph>,
which in turn is a subclass of C<odf_element>.

=head1  Paragraph creation and retrieval

=head2  Text element creation

A paragraph can be created with a given style and a given text content. The
default content is an empty string. There is not default style; a paragraph can
be created without explicit style, as long as the default paragraph style of the
document is convenient for the application. The style and the text content may
be set or changed later.

Paragraphs are instances of the C<odf_paragraph> class, that is a short name
for C<ODF::lpOD::Paragraph>.

A paragraph is created (as a free element) using the C<odf_create_paragraph>
function, with a C<text> and a C<style> optional parameters. It may be
attached later in a context through the standard C<append_element> or
C<insert_element> method:

        $p = odf_create_paragraph(
                text    => 'My first paragraph',
                style   =>'TextBody'
                );
        $context->append_element($p);

C<odf_create_paragraph()> is an exported alias for the C<create> constructor
of the C<odf_paragraph> class, so the three following instructions are
equivalent:

        $p = odf_create_paragraph(
                text => "the text", style => "stylename"
                );
        $p = odf_paragraph->create(
                text => "the text", style => "stylename"
                );
        $p = ODF::lpOD::Paragraph->create(
                text => "the text", style => "stylename"
                );

A heading may be created in a similar way using C<odf_create_heading>.
However, this constructor allows not only the C<text> and C<style> options,
but much more parameters:

=over

=item

C<level> that indicates the hierarchical level of the heading (default 1,
i.e. the top level);

=item

C<restart numbering>, a boolean which, if true, indicates that the numbering
should be restarted at the current heading (default FALSE);

=item

C<start value> to restart the heading numbering of the current level at a
given value;

=item

C<suppress numbering>, a boolean which, if true, indicates that the heading
must not be numbered (default FALSE).

=back

The option names may be used "as is" (between quotes) or with underscore
characters instead of white spaces (i.e. C<"start value"> may be replaced by
C<start_value>, and so on).

Each of these properties may be retrieved or changed later using C<get_xxx>
or C<set_xxx> accessors, where C<xxx> is the name of the optional parameter
(and where any space is replaced by a "_").

If a start value is set using the C<set_start_value> accessor, then the
C<restart numbering> boolean is silently set to C<TRUE>.

The following example creates a level 2 heading that will be numbered 5
whatever the sequence of previous headings:

        my $h = odf_create_heading(
                text                    => "The new level 2 heading"
                style                   => "Heading2",
                level                   => 2,
                'start value'           => 5,
                'restart numbering'     => TRUE
                );

A heading is an instance of C<odf_heading> (alias C<ODF::lpOD::Heading>).

=head2  Text element retrieval

Paragraphs and headings may be retrieved using dedicated context-based methods.

=head3  get_heading

Returns a heading element. By default, the returned element is the first
heading in the context. However, optional attributes allows the user to
specify search conditions:

=over

=item

C<level>: restricts the search to the headings of the given level;

=item

C<position>: The sequential zero-based position of the heading among other
headings in the order of the document; negative positions are counted
backward from the end; this option allows the application to select another
heading than the first one of the given context;

=item

C<content>: a search string (or a regexp) restricting the search space to the
headings with matching content.

=back

This instruction returns the last level 1 heading:

        $h = $context->get_heading(
                level           => 1,
                position        => -1
                );

=head3  get_headings

Takes the same arguments as C<get_heading>, without the C<position>, and returns
the list of the heading elements that meet the conditions.

Alternatively, C<get_headings()> can return all the headings I<up to> a given
level. To do so, the user must set a C<all> boolean option to C<TRUE> (knowing
its default value is C<FALSE>). As an example, the following instruction returns
all the headings whose level is not greater than 3:

        @contents = $doc->get_headings(level => 3, all => TRUE);

Without specified C<level>, C<get_headings()> returns all the headings
whatever the value of the C<all> option.

=head3  get_paragraph

A paragraph can be retrieved in a given context using C<get_paragraph> with the
appropriate C<content> and/or C<position> options like a heading, but without
the C<level> option. However, an optional C<style> parameter allows to restrict
the search to paragraphs using a given style. The example below returns the
5th paragraph using the "Standard" style and containing "ODF":

        $p = $context->get_paragraph(
                style           => "Standard",
                content         => "ODF",
                position        => 4
                );

=head3  get_paragraphs

Without argument, returns all the paragraphs in the context. Restrictions are
possible using the same options as C<get_paragraph> without, of course, the
C<position> option.

=head1  Paragraph & heading property accessors

=head2  Style

The style of a paragraph or a header may be read or changed at any time using
C<get_style> or C<set_style>. With C<set_style>, the argument is the name of
a paragraph style that may exist or that will be created later.

=head2  Text content

=head3  set_text

The paragraph/heading version of C<set_text> produces the same effects as the
common C<set_text> method (see L<ODF::lpOD::Element>), with additional features.

The tabulation marks (C<"\t">) and line breaks (C<"\n">) are allowed in the
given texts. Multiple contiguous spaces are allowed, too, and silently replaced
by the corresponding ODF-compliant constructs. For example, the instruction
below stores a multi-line content in a paragraph:

        $paragraph->set_text("First line\nSecond line\nThird line");

Caution: Remember that C<set_text> deletes any previous content in the calling
element.

=head3  get_text

Like the common C<get_text> method (see L<ODF::lpOD::Element>), the paragraph-
based version of C<get_text> returns the text content of the paragraph. However,
in a paragraph (or heading), C<get_text> processes the tabs, line breaks, and
multiple space elements in a ODF-compliant way. it returns the whole displayable
text content of the paragraph, without markup (the exported text is "flattened"
whatever the possible use or various text styles in the paragraph). However,
the various objects possibly inserted in the text, such as notes, text fields
and so on, are not exported by default.

If the C<recursive> option is set to C<TRUE>, C<get_text()> provides a flat
export of the concatenated text contents of all the elements included in the
paragraph (including notes, fields and so on).

=head2  Other properties

All the properties that may be set through C<odf_create_heading> may be read or
set later using corresponding C<get_xxx> or C<set_xxx> attributes.
These properties are allowed for headings only.

=head1  Text processing inside a paragraph

The traditional string editing methods (i.e. regex-based search & replace
functions) are available against the text content of a paragraph.

C<search()> is a element-based method which takes a search string (or a
regular expression) as argument and returns the offset of the first substring
matching the argument in the text content of the element. A null return value
means no match. In case of success, the method returns a data structure whose
attributes are the text node (C<segment>), the offset in the segment
(C<offset>), and the matching substring itself (C<match>).

The search space includes all the text children and descendants of the calling
context.

C<replace()> is a context-based method. It takes two arguments, the first one
being a search string like with C<search()>, the second one a text which will
replace any substring matching the search string. The return value of the
method is the total number of matches. If the second argument is an empty
string, every matching substring is just deleted without replacement. If the
second argument is missing, then nothing is changed, and the method just behaves
as C<count_matches()> (see below). This method is context-based, so it
recursively works on all the paragraphs, headers and spans below the calling
element; the calling element may be any ODF element, including the elements
that can't directly own a text content. It may be called at the document level.
The return value is the number of replacements done.

C<count_matches()>, whose argument is a search expression, returns the number
of matches in the context. Note that this number is not the number of elements
whose content matches the expression, because several matches may occur in the
content of the same element.

=head1  Text spans and hyperlinks

A paragraph may contain special markup elements. A I<text span> is a particular
substring whose style is not the paragraph style; it's a "sub-paragraph" with
its own style. A I<hyperlink> is a variant of text span; it associates a text
segment with a URL instead of a style.

=head2  Text spans

A style span is created through the C<set_span> method  from the object that
will contain the span. This object is a paragraph, a heading or an existing
styling span. The method must be called with a C<style> named parameter whose
value should be the name of any text style (common or automatic, existing or to
be created in the same document). C<set_span> may use a string or a regular
expression, which may match zero, one or several times the text content of
the calling object, so the spans can apply repeatedly to every substring that
matches. The string is provided through a C<filter> parameter. Alternatively,
C<set_span> may be called with given C<offset> and C<length> parameters,
in order to apply the span once whatever the content. Note that C<offset> is
an offset that may be a positive integer (starting to 0 for the 1st position),
or a negative integer (starting to -1 for the last position) if the user prefers
to count back from the end of the target. If the C<length> parameter is omitted
or set to 0 the span runs up to the end of the target content. If C<offset>
is out of range, nothing is done; if C<offset> is OK, extra length (if any)
is ignored. The following instructions create two text spans with a so-called
"HighLight" style; the first one applies the given style to any "The lpOD
Project" substring while the second one does it once on a fixed length substring
at a given offset, C<$p> being the target paragraph:

        $p->set_span(filter => 'The lpOD Project', style => 'HighLight');
        $p->set_span(offset => 3, length => 5, style => 'HighLight');

See L<ODF::lpOD::Style> for details about the text styles.

The return value of C<set_span()> is the newly created text span object (if
any). This object, whose class is C<odf_text-element> (alias
C<ODF::lpOD::TextElement>) may be used as the context for a subsequent call
of C<set_span()> (knowing that spans may be nested) or other markup insertion
methods such as C<set_hyperlink()>, C<set_bookmark()>, and so on. The return
value is C<undef> in case of failure.

C<set_span()> may work repeatedly even if C<offset> is defined, if the
C<repeat> option is set to C<TRUE>. So the instruction below applies the given
text style to I<every> matching substring whose location is after the given
offset:

        $p->set_span(
                filter  => 'lpOD',
                style   => 'HighLight',
                offset  => 15,
                repeat  => TRUE
                );

Symmetrically, C<set_span()> will not work repeatedly if C<repeat> is
explicitly set to C<FALSE>, even if C<offset> is not defined.

If either C<offset> is not defined or C<repeat> is set to C<TRUE>,
C<set_span()> returns the list of newly created text spans, or the first one
only in scalar context.

Note that C<set_span()> can't apply a style to a substring split over two or
more I<text nodes>. For example, if the given C<filter> is "Open Document" and
if there is a bookmark or any other markup element between "Open" and
"Document", there is no possible match. For the same reason, there is no
match if the substring is already split due to a previously defined span.

To illustrate this last principle, the following instruction, that should
create a span covering the whole content of the calling paragraph, will stop
at the first visible or invisible internal markup, because ".*" means the
whole content of a text node, not the whole content of the paragraph:

        $p->set_span(
                filter  => ".*",
                style   => "HighLight",
                repeat  => FALSE
                );

The numeric C<offset> is not the only area restriction parameter. Thanks to
the C<start mark> and/or C<end mark> options, this area may be delimited by
previously existing markup elements. As an example, the following sequence
applies a style to the whole text content between two bookmarks (supposedly
existing in the paragraph):

        $bm1 = $p->get_bookmark("BM1");
        $bm2 = $p->get_bookmark("BM2");
        $p->set_span(
                filter          => ".*",
                style           => "HighLight",
                'start mark'    => $bm1,
                'end mark'      => $bm2
                );

The given delimitation marks may be bookmarks, index marks, bibliography marks
or any other elements (including previously existing text spans). If
C<start mark> is set, C<end mark> is not mandatory and vice versa.

If C<start mark> and C<offset> are provided, then the offset is counted from
the position of the start mark.

Warning: A text span can cover a I<flat text> segment only; as a consequence,
C<set_span()> can't install a text span that would include any breaking
object, such as a tabulation mark ("\t"), a new line ("\n"), a multiple space,
a text bookmark, and so on.

=head2  Text hyperlinks

A hyperlink span is created through C<set_hyperlink>, which allows the
same positioning options as C<set_span()>.

However, there is a C<url> parameter instead of a C<style> one. The value of
C<url> is any kind of path specification that is supported by the end user's
ODF viewer; this value is not checked.

A hyperlink span can't contain any other span, while a style span can contain
one or more spans. As a consequence, the only one way to provide a hyperlink
span with a text style consists of embedding it in a style span.

As an example, the instruction below applies the "HighLight" text style to
every "ODF" and "OpenDocument" substring in the C<$p> context:

        $p->set_span(filter => 'ODF|OpenDocument', style => 'HighLight');

The following example associates an hyperlink in the last 5 characters of the
C<$p> container (note that the C<length> parameter is omitted, meaning that
the hyperlink will run up to the end):

        $p->set_hyperlink(offset => -5, url => 'http://here.org');

The sequence hereafter show the way to set a style span and a hyperlink for
the same text run. The style span is created first, then it's used as the
context to create a hyperlink span that spreads over its whole content:

        $s = $p->set_span(
                filter  => 'The lpOD Project',
                style   => 'Outstanding'
                );
        $s->set_hyperlink(
                filter  => ".*",
                url     => 'http://www.lpod-project.org'
                );

The C<set_hyperlink()> method allows additional options regarding the link
properties, namely:

=over

=item

C<name>: a significant name, distinct from the URL;

=item

C<title>: a link title;

=item

C<style>: a text style, corresponding to the "unvisited" state;

=item

C<visited style>: a text style, to apply when the state is "visited".

Note that the two style-related options, if set, override the default styling
for the "visited" and "unvisited" states.

=back

=head1  Bookmarks and index marks

A I<bookmark> is either a place holder that specifies a particular offset in
the text of a paragraph, or a named text segment that may spread over more than
one paragraph. An I<index mark> is a particular bookmark that may be used in
order to create a document index.

=head2  Bookmarks

A I<position bookmark> is a location mark somewhere in a text container, which
is identified by a unique name, but without any content. Its just a named
location somewhere in a text container.

By default, the bookmark is created and inserted using C<set_bookmark()>
before the first character of the content in the calling element (which may be a
paragraph, a heading, or a text span). As an example, this instruction creates
a position bookmark before the first character of a paragraph:

        $paragraph->set_bookmark("MyFirstBookmark");

This very simple instruction is appropriate as long as the purpose in only to
associate a significant and persistent name to a text container in order to
retrieve it later (with an interactive text processor or by program with lpOD or
another ODF toolkit). It's probably the most frequent use of bookmarks. However,
the API offers more sophisticated functionality.

Note that a large part of the positioning options allowed for bookmarks work
with almost all the objects that may be inserted within a text content, such
as I<index marks>, I<bibliography marks>, and others. So a basic knowledge of
the C<set_bookmark()> positioning logic is recommended, even if you don't need
to put bookmarks in your documents.

The I<offset> can be explicitly provided by the user with a C<offset>
parameter. Alternatively, the user can provide a regular expression using a
C<before> or C<after> parameter, whose value is a search string (or a regexp)
so the bookmark is set immediately before or after the first substring that
matches the expression. The code below illustrates these possibilities:

        $paragraph->set_bookmark("BM1", before => "xyz");
        $paragraph->set_bookmark("BM2", offset => 4);

This method returns the new bookmark element (that is an C<odf_element>) in
case of success, or a null value otherwise.

When the bookmark must be put at the very end of the calling element, the
C<offset> parameter may be set to C<'end'> instead of a numeric value.

For performance reasons, the uniqueness of the given name is not checked. If
needed, this check should be done by the applications, by calling
C<get_bookmark()> (with the same name and from the I<root> element) just
before C<set_bookmark()>; as long as C<get_bookmark()> returns a null value,
the given bookmark name is not in use in the context.

There is no need to specify the creation of a position bookmark;
C<set_bookmark()> creates a position bookmark by default; an additional
C<role> parameter is required for I<range bookmarks> only, as introduced later.

The first instruction in the last example sets a bookmark before the first
substring matching the given expression (here "xyz"), which is processed as a
regular expression. The second instruction sets a bookmark in the same
paragraph at a given (zero-based), so before the 5th character.

In order to put a bookmark according to a regexp that could be matched more than
once in the same paragraph, it's possible to combine the C<offset> and text
options, so the search area begins at the given C<offset>. The following example
puts a bookmark at the end of the first substring that matches a given
expression after a given offset:

        $paragraph->set_bookmark("BM3", offset => 4, after => "xyz");

Thanks to the generic C<set_attribute()> and C<set_attributes()> methods,
the user can set or unset any arbitrary attribute later, without automatic
compliance check. In addition, arbitrary attributes may be set at the creation
time (without check) using an optional C<attributes> parameter, whose content
is a hash ref of attribute/value pairs (like with C<set_attributes()>).

A bookmark can be retrieved by its unique name using C<get_bookmark()> from
any element (including the root context).

The ODF element that contains the bookmark then can be obtained as the parent of
the bookmark element, using the C<get_parent()> method from the retrieved
bookmark. Alternatively, C<get_element_by_bookmark()>, whose argument is a
bookmark name, directly returns the element that contains the bookmark. However,
a bookmark may belong to a text span, that in turn may belong to another text
span, and so on. In order to directly get the real paragraph or heading element
that contains the bookmark (whatever the possible intermediate hierarchy of
sub-containers), an additional C<get_paragraph_by_bookmark()> method is
available.

In the following example, the first instruction returns the text container
(whatever its type, paragraph, heading or text span) where the bookmark is
located, while the second one returns the paragraph or the heading that
ultimately contains the bookmark (note that in many situations both will return
the same element):

        $element = $context->get_element_by_bookmark("BM1");
        $element = $context->get_paragraph_by_bookmark("BM1");

C<get_element_by_bookmark()> may be used with a C<tag> option that specifies
either the XML tag of the needed element, or a regexp that represents several
possible elements. This feature is intended for users who have some knowledge
of the OpenDocument XML vocabulary. If C<tag> is provided,
C<get_element_by_bookmark()> returns the first element that directly or
indirectly contains the bookmark, if any. For example, the instruction below
returns the I<section> that contains the specified bookmark, knowing that
C<text:section> is the standard tag for a section:

        $section = $context->get_element_by_bookmark(
                "BM1", tag => 'text:section'
                );

The next example (using a regexp) returns the nearest object that contains the
bookmark and whose tag ends by "cell" or by "frame", practically meaning a
I<table cell> or a I<draw frame>, whose respective tags are C<table:table-cell>
and C<draw:frame>:

        $object = $context->get_element_by_bookmark(
                "BM1", tag => qr'cell$|frame$'
                );

The return value is C<undef> if the bookmark is not found in the context or if
it's not contained in a matching tag.

The C<remove_bookmark()> method may be used from any context above the
container or the target bookmark, including the document root, in order to
delete a bookmark whatever its container. The only required parameter is the
bookmark name.

A range bookmark is an identified text range which can spread across paragraph
frontiers. It's a named content area, not dependent of the document tree
structure. It starts somewhere in a paragraph and stops somewhere in the same
paragraph or in a following one. Technically, it's a pair of special position
bookmarks, so called bookmark start and bookmark end, owning the same name.

The API allows the user to create a range bookmark within an existing content,
as well as to retrieve and extract it according to its name. Range bookmarks
share some common functionality with position bookmarks

A range bookmark may be inserted using C<set_bookmark()> like a position
bookmark. However, this method must be sometimes called twice knowing that the
start and end points aren't always in the same context. In such a situation,
an additional C<role> parameter is required. The value of C<role> is either
C<start> or C<end>, and the application must issue two explicit calls with the
same bookmark name but with the two different values of C<role>. Example:

        $paragraph1->set_bookmark(
                "MyRange",
                offset  => 12,
                role    => "start"
                );
        $paragraph2->set_bookmark(
                "MyRange",
                offset  => 3,
                role    => "end"
                );

The sequence above creates a range bookmark starting at a given offset in a
paragraph and ending at another offset in another paragraph.

Knowing that the default offset is C<0>, and the last offset in a string is
C<'end'>, the following example creates a range bookmark that just covers the
full content of a single paragraph::

        $paragraph->set_bookmark(
                "AnotherBookmark", role => 'start'
                );
        $paragraph->set_bookmark(
                "AnotherBookmark", role => 'end', offset => 'end'
                );

A range bookmark may be entirely contained in the same paragraph. As a
consequence, it's possible to create it with a single call of
C<set_bookmark()>, with parameters that make sense for such a situation. If a
C<content> parameter, whose value is a regexp, is provided instead of the
C<before> or C<after> option, the given expression is regarded as covering
the whole text content to be enclosed by the bookmark, and this content is
supposed to be entirely included in the calling paragraph. So the range bookmark
is immediately created and automatically balanced. As soon as C<content> is
present, C<role> is not needed (and is ignored). Like C<before> and C<after>,
C<content> may be combined with C<offset>. In addition, the range bookmark
is automatically complete and consistent.

Note that the following instruction::

        $paragraph->set_bookmark("MyRange", content => "xyz")

does exactly the same job as the sequence below (provided that the calling
paragraph remains the same between the two instructions):

        $paragraph->set_bookmark(
                "MyRange", before => "xyz", role => "start"
                );
        $paragraph->set_bookmark(
                "MyRange", after => "xyz", role => "end"
                );

Another way to create a range bookmark in a single instruction is to provide
a list of two offsets through the C<offset> optional parameter. These two
offsets will be processed as the respective C<offset> parameters of the
start en end elements, respectively.

        $paragraph->set_bookmark("MyRange", offset => [3,15]);

When two offsets are provided, the second offset can't be before the first
one and the method fails if one of the given offsets is off limits, so the
consistency of the bookmark is secured as soon as C<set_bookmark()> returns a
non-null value with this parameter.

Alternatively, it's possible to provide a C<length> option. If this option
is set and greater than 0, it's regarded as the range. As an example, the
two following instructions produce the same effect:

        $paragraph->set_bookmark("MyRange", offset => [3, 8]);
        $paragraph->set_bookmark("MyRange", offset => 3, length => 5);

Note that if C<length> is set while C<offset> is not set, the range bookmark
will start at offset 0.

The C<offset> and C<content> parameters may be combined in order to create a
range bookmark whose content matches a given filter string in a delimited
substring in the calling element. The next example creates a range bookmark
whose content will begin before the first substring that matches a "xyz"
expression contained in a range whose the 5 first characters and the 6 last
characters are excluded:

        $paragraph->set_bookmark(
                "MyRange", content => "xyz", offset => [5, -6]
                );

When C<set_bookmark> creates a range bookmark in a single instruction, it
returns a pair of elements according to the same logic as C<get_bookmark>
(see below).

If the start offset is not before the end offset, a warning is issued and
nothing is done.

The consistency of an existing range bookmark may be verified using the
C<check_bookmark> context-based method, whose mandatory argument
is the name of the bookmark, and that returns C<TRUE> if and only if the
corresponding range bookmark exists, has defined start and end points I<and> if
the end point is located after the start point. This method returns C<FALSE>
if anyone of these conditions is not met (as a consequence, C<get_bookmark()>
may succeed while C<check_bookmark> fails for the same bookmark name). Of
course, C<check_bookmark> always succeeds with a regular position bookmark,
so, with a position bookmark, this method is just en existence check.

A range bookmark is not a single object; it's a pair of distinct ODF elements
whose parent elements may differ. With a range bookmark, C<get_bookmark()>
returns the pair instead of a single element like with a position bookmark.
Of course, the first element of the pair is the start point while the second
one is the end point. So it's possible, with the generic element-based
C<parent> method, to select the ODF elements that contain respectively the
start and the end points (in most situations, it's the same container).

The context-based C<get_element_by_bookmark>, when the given name designates
a range bookmark, returns the parent element of the start point by default.
However, it's possible to use the same C<role> options as with
C<set_bookmark()>; if the C<role> value is C<'end'>, then
C<get_element_by_bookmark()> will return the container of the end point (or
null if the given name designates a position bookmark or an non-consistent
range bookmark whose end point doesn't exist).

A C<get_bookmark_text()> context-based method, whose argument is the name of a
range bookmark, returns the text content of the bookmark as a flat string,
without the structure; this string is just a concatenation of all the pieces of
text occurring in the range, whatever the style and the type of their
respective containers; however, the paragraph boundaries are replaced by blank
spaces. Note that, when called with a position bookmark or an inconsistent
range bookmark, C<get_bookmark_text()> just returns an null value, while it
always returns a string (possibly empty) when called from a regular range
bookmark.

A range bookmark (consistent or not) may be safely removed through the
C<remove_bookmark()> method (which deletes the start point and the end point).

A range bookmark can be safely processed only if it's entirely contained in the
calling context. A context that is not the whole document can contain a bookmark
start or a bookmark end but not both.  In addition, a bookmark spreading across
several elements gets corrupt if the element containing its start point or its
end point is later removed.

The C<remove_bookmark()> method (which can be used at any level, including the
document root) allows the applications to safely remove balanced and
non-balanced range bookmarks. Nothing is done if the given bookmark is not
entirely contained in the calling context element. The return value is C<TRUE>
if a bookmark has really been removed, or C<FALSE> otherwise.

In addition, C<clean_marks()> automatically removes non-balanced range
bookmarks (as well as non-balanced index marks). Caution: this method is
potentially harmful, knowing that a bookmark may be non-balanced in a given
element while it's consistent at a higher level, knowing that its start and end
points may belong to different paragraphs. On the other hand, it's always safe
from the document root or body element.

=head2  Reference marks and fields

=head3  Reference marks

References marks are created according using C<set_reference_mark()>, according
to the same logic as bookmarks. The first argument is the unique reference name
and all the options are the same as with C<set_bookmark()>. Note that it's
possible to create I<point references> as well as I<range references>.

When setting a range reference, it's recommended to put the start and the end
in the same paragraph or heading.

Reference marks may be retrieved in the same way as bookmarks through the
context-based C<get_reference_mark()> and C<get_reference_marks()> methods.

=head3  Reference fields

A reference mark, like a bookmark, may be the target of a I<reference field>,
that is a particular dynamic text field. A reference field is intended to
display an information regarding a reference mark that is located elsewhere.
A reference field may be set using C<set_reference()> with the same positioning
options as bookmarks or text fields, and the following specific named
parameters:

=over

=item

C<type>: the type of target, that may be C<reference> (the default) or
C<bookmark>;

=item

C<name>: the name of the target bookmark or reference mark;

=item

C<format>: specifies what information about the reference is displayed;
supported values are C<page> (the default), C<chapter>, C<direction>, C<text>,
C<category-and-value>, C<caption>, and C<value>; see section 6.6.5 in ODF 1.1
specification for details about these values.

=back

As an example, the following sequence, assuming that C<$p1> and C<$p2> are two
distinct paragraphs, puts a reference mark in C<$p1> and inserts a field that
displays the chapter number of C<$p1> immediately after a given substring in
C<$p2>:

        $p1->set_reference_mark("Here");
        $p2->set_reference(
                type    => 'reference',
                format  => 'chapter'
                name    => "Here",
                after   => "see chapter "
                );

=head2  Index marks

Index marks may be handled like bookmarks but their functionality differs.
There are three kinds of index marks, namely:

=over

=item

C<lexical> marks, whose role is to designate text positions or ranges in
order to use them as entries for a lexical (or alphabetical) index;

=item

C<toc> marks, created to become the source for tables of contents (as soon
as these tables of contents are generated from TOC marks instead of headings);

=item

C<user> marks, which allow the user to create custom indices (which could be
ignored by the typical TOC or lexical index generation features of the
office applications).

=back

An index mark, just like a text bookmark, is either a mark associated to an
offset in a text, or a pair of location marks that defines a delimited range
of text.

An index mark is created in place using the C<set_index_mark()> context-based
method, according to the same basic logic as C<set_bookmark()>, with some
important differences:

=over

=item

because an index mark is not a named object, the first argument of
C<set_index_mark> is not really a name, like a bookmark name; this
argument (which remains mandatory) is either a technical identifier, or
a significant text, according to the kind of index mark;

=item

for a position index mark (which, by definition, has no text content), the
first argument is a text string that is displayed in the associated index
(when this index is generated);

=item

for a range index mark (which, by definition, has a text content), the first
argument is only a meaningless but unique key that is internally used in order
to associate the two ODF elements that represent the start point and the end
point of the range; this key should not be displayed by a typical interactive
text processor, and is not reliable as a persistent identifier knowing that
an ODF-compliant application could silently change it as soon as the document
is edited;

=item

an additional C<type> option, whose possible values are C<'lexical'>, C<'toc'>,
and C<'user'>, specifies the functional type; the default is C<'lexical'>;

=item

when the C<'user'> type is selected, an additional C<'index name'> parameter is
required; its value is the name of the user-defined index that will (or could)
be associated to the current index entry; this name could be regarded as the
arbitrary name of an arbitrary collection of text marks;

=item

According to the ODF 1.1 specification (§7.1.3), lexical bookmarks may have
additional keys, so-called C<key1> and C<key2>, and a boolean C<main entry>
attribute; these optional properties may be set (without automatic check)
using the optional C<attributes> parameter that allows the applications to
add any arbitrary property to a bookmark or an index mark (the value of this
parameter is a attribute/value hash ref);

=item

if the C<index name> argument is provided, the mandatory value of C<type>
is C<'user'>; as a consequence, if C<index name> is set, the default C<type>
becomes C<'user'> and the C<type> parameter is not required;

=item

every C<'toc'> or C<'user'> index mark owns a I<level> property that specifies
its hierarchical level in the table(s) of contents that may use it; this
property may be provided using a C<level> optional parameter; its default
value is C<1>;

=item

according to the ODF 1.1 specification, the range of an index mark can't
spread across paragraph boundaries, i.e. the start en end points must be
contained in the same paragraph; as a consequence, a range index mark may
(and should) be always created using a single C<set_index_mark>;

=item

like C<set_bookmark>, C<set_index_mark> returns a pair of ODF elements
when it creates a range index mark; if the application needs to set particular
properties (using the C<set_attribute> generic method or otherwise) to the
index mark, the first element of the pair (i.e. the start point element) must
be used.

=back

See C<set_bookmark()> for details about the index mark positioning options.

The example hereafter successively creates, in the same paragraph, a range TOC
mark, two range index marks associated to the same user-defined index, and a
lexical position index mark at the default offset (i.e. before the first
character of the paragraph):

        $paragraph->set_index_mark(
                "id1", type => "toc", offset => [3,5]
                );
        $paragraph->set_index_mark(
                "id2", index_name => "OpenStandards", content => "XML"
                );
        $paragraph->set_index_mark(
                "id3", index_name => "OpenStandards", content => "ODF"
                );
        $paragraph->set_index_mark(
                "Go There", type => "lexical"
                );

Note that the last instruction (unlike the preceding ones) uses a possibly
meaningful text as the first argument instead of an arbitrary technical
identifier. Because this instruction creates a lexical index entry, the given
text will appear in the document as a reference to the paragraph as soon as a
standard lexical index is generated (by the current program or later by an
end-user office software).

There is a C<get_index_marks()> context-based method that allows the
applications to retrieve a list of index entries present in a document or in a
more restricted context. This method needs a C<type> parameter, whose possible
values are the same as with C<set_index_mark()>, in order to select the kind of
index entries; the C<'lexical'> type is the default. If the C<'user'> type is
selected, the name of the user-defined index must be provided too,
through a C<index name> parameter. However, if C<index name> is provided,
the C<'user'> type is automatically selected and the C<type> parameter is not
required.

The following example successively produces three lists of index marks, the
first one containing the entries for a table of contents, the second one the
entries of a standard lexical index, and the third one the entries dedicated
to an arbitrary user-defined index::

        @toc = $document->get_root->get_index_marks(type => 'toc');
        @alphabetical_index = document->get_root->get_index_marks;
        @foo_index = $document->get_root->get_index_marks(
                index_name => "foo"
                );

=head1  Bibliography marks

A I<bibliography mark> is an element that specifies a relationship between a
particular place in a paragraph and a bibliographic data structure. The lpOD
API provides methods allowing to handle such objects.

A bibliography mark is a particular index mark. It may be used in order to
store anywhere in a text a data structure which contains multiple attributes but
whose only one particular attribute, so-called the I<identifier> is visible at
the place of the mark. All the other attributes, or some of them, may appear in
a bibliography index, when such an index is generated (according to index
format).

A bibliography mark is created using the C<set_bibliography_mark> method from
a paragraph, a heading or a text span element. Its placement is controlled with
the same arguments as a position bookmark, i.e. C<offset>, C<before> or
C<after> (look at the I<Bookmarks> section for details). Without explicit
placement parameters, the bibliography mark is inserted at the beginning of the
calling container.

Unlike C<set_bookmark()>, C<set_bibliography_mark()> doesn't require a name as
its first argument, but it requires a named C<type> parameter whose value
is one of the publication types listed in the §7.1.4 of the ODF 1.1
specification (examples: C<'article'>, C<'book'>, C<'conference'>,
C<'techreport'>, C<'masterthesis'>, C<'email'>, C<'manual'>, C<'www'>, etc).
This predefined set of types is questionable, knowing that, for example, the
standard doesn't tell us if the right type is C<'www'> or C<'manual'> for, say,
a manual that is published through the web, but the user is responsible for the
choice.

Beside the C<type> parameter, a C<identifier> parameter (that is not a real
identifier in spite of its name) is supported. This so-called C<identifier>,
unlike a real identifier, is a label that will be displayed in the document at
the position of the bibliography entry by a typical ODF-compliant viewer or
editor and that will provide the end-user with a visible link between the
bibliography mark in the document body and a bibliography index later generated
elsewhere. Nothing in the ODF 1.1 specification prevents the applications from
creating the same bibliography mark repeatedly, and from inserting different
bibliography marks with the same "identifier".

The full set of supported parameters correspond to the list of possible
attributes of the bibliography mark element, defined in the §7.1.4 of the
ODF 1.1 specification. All them are C<text:> attributes, but
C<set_bibliography_mark> allows the use of named parameters without the
C<text> prefix (examples: C<author>, C<title>, C<editor>, C<year>, C<isbn>,
C<url>, etc). The instruction below inserts in a paragraph, immediately after
the first occurrence of the "lpOD documentation" substring, a bibliography
entry that represents the lpOD documentation, and whose visible label at the
insertion point could be something like "[lpOD2010]" in a typical document
viewer:

        $paragraph->set_bibliography_mark(
                identifier      => "lpOD2010",
                type            => "manual",
                after           => "lpOD documentation",
                year            => "2010",
                month           => "december",
                url             => "http://docs.lpod-project.org",
                editor          => "The lpOD Team"
                );

The positioning parameters as the same as with C<set_bookmark()> (the C<after>
parameter is used in this example), according to the same logic as for a
position bookmark.

C<set_bibliography_mark()> returns an ODF element whose any property may be
set or changed later through the generic element-based C<set_attribute()>
method.

Knowing that there is no persistent unique name for this class of objects, there
is a context-based C<get_bibliography_marks()> method that returns the list of
all the the bibliography marks. If this method is called with a string argument
(which may be a regexp), the search is restricted to the entries whose so-called
C<identifier> property is defined and matches this argument. Each element of
the returned list (if any) may be then checked or updated using the generic
C<get_attribute()>, C<get_attributes()>, C<set_attribute()>, and
C<set_attributes()> methods.

=head1  Notes

=head2  Footnote and endnote creation

These notes are created in place using the element-based C<set_note()> method,
that requires a note identifier (unique for the document) as its first argument,
and the following note-specific parameters:

=over

=item

C<class> or C<note_class>: the class option, whose default is C<footnote>;

=item

C<citation>: the citation mark (i.e. a formatted string representing the
sequence number, see "Note citation" in ODF 1.1 §5.3.1);

=item

C<label>: the optional text label that should be displayed at the insertion
point of the note; if this parameter is omitted, the displayed note label will
be an automatic sequence number;

=item

C<body>: the content of the note, provided either as a list of one or more
previously created ODF content elements (preferentially paragraphs), or as an
already available note body element (produced, for example, by cloning the
body of another note);

=item

C<text>: the content of the note, provided as a flat character string;

=item

C<style>: the name of the paragraph style for the content of the note.

=back

The C<text> and C<style> parameters are ignored if C<body> is provided,
because C<body> is supposed to be a list of one or more paragraphs, each one
with its own style and content. The C<body> option allows the applications to
reuse an existing content for one or more notes in one or more documents.
Without the C<body> parameter, a paragraph is automatically created and filled
with the value of C<text>. If neither C<body> nor C<text> is provided, the
note is created with an empty paragraph.

The list of ODF elements provided through the C<body> parameter may contain
almost any content object; neither the OpenDocument schema nor the lpOD level 1
API prevents the user from including notes into a note body; however the lpOD
team doesn't recommend such a practice.

It's possible to create a note as a free element with C<odf_create_note>, so it
can be later inserted in place (and replicated for reuse in several locations
in one or more documents), using general purpose insertion methods such as
C<insert_element()>.

By default, C<set_note()> inserts the new note at the beginning (i.e. as the
first child element) of the calling element. However, it's possible to specify
another position within the text content of the element, using the same
positioning options as the C<set_bookmark()> method, namely C<position>,
C<before>, C<after>, and so on (see C<set_bookmark()>).

As an example, the following instruction inserts a footnote whose citation mark
is an asterisk, with a given text content, immediately after the "xyz" substring
in a paragraph:

        $paragraph->set_note(
                "note0004",
                class   => 'footnote',
                after   => 'xyz',
                label   => '*',
                text    => 'The footnote content',
                style   => 'Note body'
                );

C<set_note()> returns the newly created object, that is available for later
use.

=head2  Footnote and endnote retrieval

Once set somewhere in a document, a note may be retrieved the context-based
C<get_note()> method, with the note identifier as argument.

It's possible to extract a list of notes using the context-based C<get_notes()>.
Without argument, this method returns all the notes of the context. However,
it's possible to provide the C<class>, C<citation>, and/or C<label> parameters
in order to select the notes that match them. The following example extract
the endnotes whose citation mark is "5" in a given section:

        @end_notes = $section->get_notes(
                class           => "endnote",
                citation        => "1"
                );

This method may allow the users to retrieve a note without knowledge of its
identifier.

=head2  Footnote and endnote methods

=head3  Read accessors

=over

=item

C<get_id()> the note identifier (generic element method);

=item

C<get_class()> the note class;

=item

C<get_citation()> the note citation;

=item

C<get_label()> the note label;

=item

C<get_body()> the root of the note body, as a single container; this object may
be used as a context element for appending or removing any object in the note
body; the real content is made of the children elements of the body; it may be
cloned in order to be reused as the body of another note in the same document
or elsewhere.

=back

=head3  Write accessors

=over

=item

C<set_id(new_id)> changes the identifier (generic element method); be careful,
C<set_id()> with a null value erases the identifier (but, with a defined value,
allows to restore it at any time).

=item

C<set_class(footnote|endnote)> allows to turn a footnote into a endnote or
vice versa.

=item

C<set_citation()> changes the note citation mark;

=item

C<set_label(new_label)> changes the note label;

=item

C<set_body()> takes the same kinds of content as the C<body> parameter of
C<set_note()>; provides the note with a new body; any previous content is
deleted and replaced; if C<set_body()> is used without argument or with a null
value, the previous content is replaced by a single empty paragraph.

=back

=head2  Annotation creation

An annotation is particular note that has neither identifier nor citation
mark, but which may be put like a footnote or a endnote at a given offset in a
given text container. On the other hand, it stores a date and an author's name.

Annotations are created using C<set_annotation()>, that takes the same
positioning parameters as C<set_note()> and C<set_bookmark()>, and the
following other parameters:

=over

=item

C<date>: the date/time of the annotation (ISO-8601 format); if this
parameter is omitted, the current system date applies by default;

=item

C<author>: the name of the author of the annotation (which may be an
arbitrary application-provided string); if this parameter is omitted, lpOD
tries to set it to the user name of the process owner and, if such an
information is not available in the run time environment, the annotation
is created with an empty string as the author name (not recommended);

=item

C<content>: a list of one or more regular text paragraphs that will become
the content of the annotation (beware, unlike C<set_note()>,
C<set_annotation()> requires a list of paragraphs and doesn't accept a
previously existing note body or other non-paragraphs ODF objects);

=item

C<text>: a flat string, that will become the text content of the
annotation; if C<text> and C<content> are both provided, the C<text> value
will become the content of the first paragraph of the annotation;

=item

C<style>: specifies a paragraph style for the content.

=back

The example below inserts a "Hello" annotation after the 4th character of a
paragraph:

    $para->set_annotation(text => "Hello", offset => 4);

C<set_annotation()> returns the newly created object, that is available for
later use.

=head2  Annotation retrieval

Annotations may be selected is through the context-based C<get_annotations()>
method that takes C<date> and C<author> as optional parameters.

Without parameter, this method returns the full list of the annotations that
appear in the context. The use of one or two of the optional parameters allows
to restrict the list according to the given C<date> and/or C<author>.

While a typical human writer using an interactive editing application should
never be able to put two annotations in the same time in the same document,
an automatic document processing application can do that. So the date/author
combination should not be regarded as an absolute identifier; as a
consequence, C<get_annotations()> always returns a list (possibly containing
a single paragraph or nothing).

=head2  Annotation methods

=head3  Read accessors

=over

=item

C<get_date()> returns the stored date.

=item

C<get_author()> returns the stored author's name.

=item

C<get_content()> returns the content as a list of paragraph(s).

=back

=head3  Write accessors

=over

=item

C<set_date(new_date)> changes the stored date; without arguments, the current
date applies.

=item

C<set_author()> changes the stored author's name; without argument, the process
owner applies.

=item

C<set_content()> replaces the current content using the argument, that is a
list of one or more paragraphs.

=back

An annotation object may be used as a regular context element in order to
change its content through generic context-based element insertion, deletion of
updating methods. No particular check is done, so the user should ensure that
inserted elements are always paragraphs.

=head1  Tracked changes

=head2  Tracked change retrieval

lpOD applications can retrieve all the change tracking data which may have been
stored in text documents by ODF-compliant editors. On the other hand, lpOD
doesn't provide any automatic tracking of the changes made by lpOD-based
applications.

A tracked change may be retrieved in a document using the C<get_change()> and
C<get_changes()> document-based methods.

Every tracked change is stored as a ODF change object that owns the following
attributes:

=over

=item

C<id>: the identifier of the tracked change (unique for the document);

=item

C<date>: the date/time of the change (ISO-8601 format);

=item

C<author>: the name of the user who made the change.

=back

An change may be individually retrieved using C<get_change()> with a change
identifier as argument.

The C<get_changes()> method, without argument, returns the full list of
tracked changes. The list may be filtered according to C<date> and/or C<author>
optional parameters.

If a single date is provided as the C<date> parameter, then the result set
contains only tracked change elements that exactly match it, if any. However
the user may specify a time interval by providing a list of two dates as the
C<date> parameter; so any tracked change whose date belongs to the given
interval is candidate. An empty string, or a 0 value, is allowed as start or
end date, meaning that there is no inferior or superior limit.

C<get_changes()> returns only the tracked changes whose author exactly matches
the given C<author> parameter, if this parameter is set.

The document-based C<get_change()> and C<get_changes()> methods look for
tracked changes in the document C<CONTENT> part only, and works with text
documents only.

In addition, lpOD provides C<get_change()> and C<get_changes()> as context
methods, allowing the applications to call them from any arbitrary element, so
the search is directed and restricted to a particular context. If the calling
element is not able to track the changes, these methods always return nothing
but they are neutral. If the calling element contains tracked changes, they
work like their document-based versions in the given context. This feature
allows the users to retrieve tracked changes in page headers and footers,
knowing that these changes are registered in the contexts of the corresponding
page style definitions, and not in the document content.

=head2  Tracked change methods

Each individual tracked change object, previously selected, own the following
methods:

=over

=item

C<delete()>: deletes the tracked change, i.e. removes any persistent information
about the tracked change object from the document.

=item

C<get_id()>: returns the identifier.

=item

C<get_date()>: returns the date.

=item

C<get_author()>: returns the author's name.

=item

C<get_type()>: returns the type of change, that is C<insertion>, C<deletion>,
or C<format-change>.

=item

C<get_deleted_content()>: returns the content of the deleted content as a list
of ODF elements, if the change type is C<deletion> (and returns a null value
otherwise).

=item

C<get_change_mark()>: returns the position mark of the change; if the change
type is C<deletion>, this object is located at the place of the deleted content;
if the change type is C<insertion> or C<format-change>, it's located at the
beginning of the affected content.

=item

C<get_insertion_marks()>: if the change type is C<insertion> or
C<format-change>, returns a pair of position mark elements, respectively located
at the beginning and at the end of the affected content (this pair of elements
may be used in a similar way as the start and end elements of a range bookmark,
in order to determine the limits of the affected content); it returns nothing
if the change type is C<deletion>.

=back

=head1  Text Fields

A I<text field> is a special text area, generally short-sized, whose content may
be automatically set, changed or checked by an interactive editor or viewer
according to a calculation formula and/or a content coming from somewhere
in the environment.

A I<table cell> may be regarded as an example of field, according to such a
definition. However, while a table cell is always part of a table row that is in
turn an element in a table, a I<text field> may be inserted anywhere in the
content of a text paragraph.

=head2  Common field-related features

=head3  Field creation and retrieval

A text field is created "in place" using the C<set_field()> element-based
method from a text container that may be a paragraph, a heading or a span;
C<set_field()> requires a first argument that specifies the kind of
information to be associated (and possibly displayed) with the field.

Regarding the positioning, this method works in a similar way as
C<set_bookmark()> or C<set_index_mark()> introduced in the I<Bookmarks and
index marks> section.

By default, the field is created and inserted  before the first character of
the content in the calling element. As an example, this instruction creates
a C<title> field (whose role is to display the title of the document) before
the first character of a paragraph:

        $paragraph->set_field("title");

A field may be positioned at any place in the text of the host container; to do
so, an optional C<offset> parameter, whose value is the offset (i.e. character
sequential position) of the target, may be provided. The value of this parameter
is either a positive position, zero-based and counted from the beginning, or a
negative position counted from the end. The following example puts a C<title>
field at the fifth position and a C<subject> field 5 characters before the
end:

        $paragraph->set_field("title", offset => 4);
        $paragraph->set_field("subject", offset => -5);

The C<set_field()> method allows field positioning at a position that depends
on the content of the target, instead of a position. Thanks to a C<before> or
a C<after> parameter, it's possible to provide a regexp that tells
to insert the new field just before of after the first substring that
matches a given filter. The next example inserts the document subject after
a given string:

        $paragraph->set_field(
                "subject",
                after   => "this paper is related to "
                );

More generally, C<set_field()> allows the same positioning options as
C<set_bookmark()> for simple position bookmarks.

In addition, C<set_field()> allows a C<search> (or C<replace>) parameter
that specifies a substring that should be I<replaced> by the field.

C<set_field()> returns the created ODF element in case of success, or null if
(due to the given parameters and the content of the target container) the field
can't be created.

A text field can't be identified by a unique name or ID attribute and can't be
selected by coordinates in the same way as a cell in a table. However, there is
a context-based C<get_fields()> method that returns, by default, all the text
field elements in the calling context. This method, when called with a single
C<content> parameter, that specifies the associated content, returns the fields
that match the given kind of content only, if any. For example, this instruction
returns all the page number fields in the document body:

        $document->get_body->get_fields("page number");

=head3  Field data types

The value of a field has a data type. The default data type is C<string>, but
it's possible to set any ODF-compliant data type as well, using the optional
parameter C<type>. According to ODF 1.1, §6.7.1, possible types are C<float>,
C<percentage>, C<currency>, C<date>, C<time>, C<boolean> and, of course,
C<string>.

If the selected C<type> is C<currency>, then a C<currency> additional
parameter is required, in order to provide the conventional currency unit
identifier (ex: EUR, USD). As soon as a C<currency> parameter is set,
C<set_field()> automatically selects C<currency> as the field type (so the
C<type> parameter may be omitted).

Note that for some kinds of fields, the data type is implicit and can't be
selected by the applications; in such a situation, the C<type> parameter, if
provided, is just ignored. For example, a C<title> or C<subject> field is
always a string, so its data type is implicit and can't be set.

=head3  Common field properties and methods

Some fields may be created with an optional C<fixed> boolean parameter, that
is C<'false'> by default but, if C<'true'>, means that the content of the field
should not be automatically updated by the editing applications. For example,
a C<date> field, that is (by default) automatically set to the current date by
a typical ODF editor each time the document is updated is no longer changed as
long as its C<fixed> attribute is C<true>. This option is allowed for some
kinds of text fields.

A numeric text field (ex: date, number) may be associated with a display format,
that is identified by a unique name and described elsewhere through a numeric
style; this style is set using the C<style> parameter with C<set_field()>.

While a field is often inserted in order to allow a viewer or editor to set an
automatically calculated value, it's possible to force an initial content (that
may be persistent if C<fixed> is true) using the optional C<value> and/or
C<text> parameters. If the data type is C<string>, the C<value> is the same
as the C<text>. For a C<date> or a C<time>, the value is stored in ISO-8601
date format. For other types, the C<value> is the numeric computable value
of the field. The C<text>, if provided, is a conventional representation of
the value according to a display format.

Text fields use a particular implementation of the generic C<get_text()>
method. When called from a text field element, this method returns the text of
the element (as it could have been set using the C<text> property), if any.
If the element doesn't contain any text, this method returns the value "as is",
i.e. without formatting.

The generic C<set_text()> method allows the applications to change the C<text>
content of the element at any time.

=head2  Document fields

According to the ODF vocabulary, document fields are text fields that I<"can
display information about the current document or about a specific part of the
current document">.

This definition could be extended knowing that some so-called I<document fields>
may host contents that are not really information about the document.

The kind of document field is selected using the mandatory argument of
C<set_field()> or C<get_fields()>.

The whole set of allowed document fields is described in the section 6.2 of the
ODF 1.1 specification. Some of them are introduced below with their associated
properties (the so-called I<content key> means the field kind selector that must
be provided when creating a field with C<set_field()>).

=head3  Date fields

Content key: C<date>. Supports C<fixed> (that should preserve the stored date
from automatic change each time the document is edited).

A date field may contain either the current date or, if C<fixed>, an arbitrary
other date.

A date field may be adjusted by a certain time period, which is specified using
the C<adjust> parameter. If the time period is negative, it gets subtracted
from the value of the date field, yielding a date before the current date.
The value of C<adjust> must be a valid duration.

This example inserts a field that displays the date of the day before
yesterday, due to a C<date adjust> value that specified a negative value of
48 hours, 0 minutes and 0 seconds:

        $paragraph->set_field(
                "date",
                style   => "DateStyle",
                adjust  => "-PT48H00M00S"
                );

Note that the display format is controlled by the given style (that is, of
course, a date style), and that a date field may be more precise than the date
of the day; whatever the displayed information, a date field is able to store
a full date and time value.

=head3  Time fields

Content key: C<time>. Supports C<fixed>.

A time field behaves like a date field, but it stores the current time or an
arbitrary fixed time only. The C<adjust> parameter, if provided, must be set
with a valid time duration, like with a date field.

=head3  Page number fields

Content key: C<page number>. Supports C<fixed>.

This field displays, by default, the current page number. If C<fixed>, it can
contain an arbitrary other page number. It allows an C<adjust>, telling the
editing applications to display the number of another page, if this page exists.
In addition, it supports a C<select> argument that may be set to C<current>
(the default), C<previous>, or C<next>, and that specifies if the value is
the number of the current, the previous or the next page.

=head3  Page continuation fields

Content key: C<page continuation>.

This field conditionally displays a continuation string if the current page is
preceded or followed by another page. It requires a C<text> parameter, that is
the continuation text to display, and a C<select> parameter, that specifies
what is the page whose existence must be checked.

The example below creates a field that displays "See next page" if and only if
the current page is not the last one:

        $paragraph->set_field("page continuation", select => "next");

=head3  Sender and Author fields

Content key: various (see below). Supports C<fixed>.

The API allows to set various fields whose purpose is to display in the document
body or in the page headers or footers some information whose source is not
precisely specified but which regard the so-called "sender" and "author" of the
document. Some of this information may come from the document metadata.

The general form of the corresponding content keys is C<sender xxx> or
C<author yyy>, where "xxx" may be C<firstname>, C<lastname>, C<initials>,
C<title>, C<position>, C<email>, C<phone private>, C<fax>, C<company>,
C<phone work>, C<street>, C<city>, C<postal code>, C<country>,
C<state or province>, and "yyy" may be C<name> or C<initials>.

Every sender and author field is created with the appropriate content key and
the optional C<fixed> flag only.

The following example tells the editing applications to print the initials
of the document sender (if such an information is available) immediately after
a given string:

        $paragraph->set_field("sender initials", after => "Issued by ");

Of course, every C<sender-> or C<author-> field may be C<fixed> and can
display a given value provided using the C<text> optional parameter.

=head3  Chapter and sheet name fields

Content key: C<chapter> or C<sheet name>.

A chapter field displays the name and/or the number of the current heading in
a document where chapters make sense, while sheet name fields, in spreadsheet
documents, display the name of the current sheet (or table).

For a chapter field, C<set_field()> allows two parameters, namely C<display>
and C<level>:

=over

=item

C<display> specifies the kind of information related to the current chapter
that the field should display; possible values are C<number>, C<name>,
C<number-and-name>, C<plain-number>, C<plain-number-and-name> (see ODF 1.1
§6.2.7);

=item

C<level> is an integer value that specifies the level of the heading that is
referred to by the field; default is 1.

=back

This examples inserts a field that displays the name of the current level 1
heading::

        $paragraph->set_field("chapter", level => 1, display => "name");

For a sheet name field, no parameter but the C<sheet name> argument is needed;
the field just displays the name of the current sheet. Note that this field
makes sense for spreadsheet documents only but that the calling element for
C<set_field()> should be a paragraph attached to a cell and not a cell, knowing
that a text fields belongs to a paragraph. Example::

        $paragraph->set_field("sheet name");

=head2  Declared variable fields

A text field may be associated to a so-called "variable", that is, according to
ODF 1.1 (§6.3) a particular user-defined field declared once with an unique name
and used at one or several places in the document. However, the behavior of such
a variable is a bit complex knowing that its content is not set once for all.

A variable may appear with a content at one place, and with a different content
at another place. It should always appear with the same data type. However, the
ODF 1.1 specification is self-contradictory about this question; it tells:

I<"A simple variable should not contain different value types at different places
in a document. However, an implementation may allow the use of different value
types for different instances of the same variable.">

More precisely, ODF allows several kinds of variables, including so-called
I<simple>, I<user> and I<sequence> variables. The present lpOD level 1 API
supports the two first categories. While a I<simple> variable may have
different values (and, practically, different types) according to its display
fields, a I<user> variable displays the same content everywhere in the document.

In order to associate a field with an existing variable, C<set_field()> must be
used with the first argument set to C<variable>, and an additional
C<name> parameter, set to the unique name of the associated variable, is
required. If the associated variable is a I<user> variable, the C<value> and
C<type> parameters are not allowed. If the variable is I<simple>, then it's
possible to set a specific value and/or type, with the effects described
hereafter. The associated variable may not exist when the field is created (it
may be created later), so it's not automatically checked when the field is
created through C<set_field()>.

The following example sets a field that displays the content of a declared
variable whose name is supposed to be "Amount":

        $paragraph->set_field("variable", name => "Amount );

When a field associated to a I<simple> variable is inserted using
C<set_field()>, its content is set, by default, to the existing content and
type of the variable. If a C<value> and/or C<text> parameter is provided, the
field takes this new content, which becomes the default content for subsequent
fields associated to the same variable, but the previous fields keep their
values. The same apply to the field type, if a new C<type> is provided. Beware,
by I<subsequent> and I<previous> we mean the fields that precede or follow the
field that is created with a changed content in the order of the document, not
in the order of their creation.

It's possible to insert a variable-based field somewhere without displaying its
value through a text viewer. An optional C<display> parameter may be set to
C<none>, that makes the field invisible, or to C<value> (the default) to allow
the GUI-based applications to display the value.

On the other hand, all the fields associated to a I<user> variable take the same
value. Each time the content of the variable is changed, all the associated
fields change accordingly. The API doesn't allow the application to change this
content through the insertion of an associated field. If needed, the variable
content may be changed explicitly using another method.

If the lpOD-based application needs to install a variable that doesn't exist,
it must use the document-based C<set_variable()> method, that takes a mandatory
first argument that is its unique name, a C<type> (whose default is C<string>)
and of course a C<currency> parameter if C<type> is C<currency>. Because
C<set_variable()> doesn't set anything visible in the document, it doesn't take
any positioning or formatting parameter. A C<value> parameter is needed in
order to set the initial content of the variable.

The example below "declares" the variable that is used by a text field in the
previous example::

        $document->set_variable(
                "Amount",
                type    => "float",
                value   => 123
                );

A C<class> parameter may be provided to select the C<user> or C<simple> kind
of variables; the default is C<user>.

A declared variable may be retrieved thanks to its unique name, using the
C<get_variable()> document-based method with the name as argument, and a named
C<class> parameter that restricts the search to the C<user> or C<simple>
variables. If C<class> is not provided, C<get_variable()> looks among both
the C<user> and C<simple> variables.

The returned object, if any, provides C<get_xxx()>- and C<set_xxx()>-like
accessors, where C<xxx> stands for C<value>, C<type>, or C<currency>, that
allow the user to change these properties at any time.

A document-based C<get_variables()> method, with a C<class> named parameter,
returns all the variables of the given variable class; without parameter, it
returns the list of the C<user> and C<simple> variables.

=head1	AUTHOR/COPYRIGHT

Developer/Maintainer: Jean-Marie Gouarne L<http://jean.marie.gouarne.online.fr>
Contact: jmgdoc@cpan.org

Copyright (c) 2010 Ars Aperta, Itaapy, Pierlis, Talend.
Copyright (c) 2011 Jean-Marie Gouarne.

This work was sponsored by the Agence Nationale de la Recherche
(L<http://www.agence-nationale-recherche.fr>).

License: GPL v3, Apache v2.0 (see LICENSE).

=cut
