NAME
    GraphViz2::Abstract::Util::Constants - Constants used by
    "GraphViz2::Abstract::*"

VERSION
    version 0.001000

CONSTANTS
    In the GraphViz documentation <http://www.graphviz.org/content/attrs>,
    there are a few default values which are used multiple times, and the
    following constants refer to them in one way or another.

    "EMPTY_STRING"
        This simply returns an empty string, and is not likely to change.

            ""

    "FALSE"
        Where the specification shows "false" as a default value, this
        module instead returns the string "false"

        This is because under the hood, GraphViz2 doesn't support values for
        attributes other than defined ones.

        So its assumed that GraphViz, under the hood, interprets the string
        "false" the same as the boolean condition "false";

    "TRUE"
        Where the specification shows "true" as a default value, this module
        instead returns the string "true"

        Its assumed that GraphViz, under the hood, interprets the string
        "true" the same as the boolean condition "true", for similar reasons
        "false" is.

    "NONE"
        In the GraphViz docs, a few items have a default value specified as:

            <none>

        This item was confusing in the specification, and it wasn't clear if
        it was some sort of magic string, or what.

        Internally, we use a special value, a reference to a string "none"
        to represent this default.

        For instance:

            my $v = Edge->new()->target();

            ok( ref $v, 'target returned a ref' );
            is( ref $v, 'SCALAR', 'target returned a scalar ref' );
            is( ${ $v }, 'none', 'target returned a scalar ref of "none"' );

        However, because its not known how to canonicalize such forms, those
        values are presently not returned by either "as_hash" methods.

        So as a result:

            my $v = Edge->new( color => \"none" )->as_hash()

        Will emit an empty hash. ( Despite "none" being different from the
        default ).

        Also:

            my $v = Edge->new( color => \"none" )->as_canon_hash()

        Will not emit a value for "color" in its output, which may have the
        undesirable effect of reverting to the default, "black" once
        rendered.

    "UNKNOWN"
        On the GraphViz documentations, there were quite a few fields where
        the defaults were simply not specified, or their values were
        cryptic.

        Internally, those fields have the default value of "\"unknown""

        Like "none", those fields with those values will not be emitted
        during hash production.

AUTHOR
    Kent Fredric <kentfredric@gmail.com>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2013 by Kent Fredric
    <kentfredric@gmail.com>.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

