# MIME::Field::ParamVal

This module is ALPHA code, which means that public interfaces are largely untested, and may change in future releases. Use with caution! Please report any errors back to eryq@zeegee.com as soon as you can.

- NAME
- SYNOPSIS
- DESCRIPTION
- PUBLIC INTERFACE

## NAME

MIME::Field::ParamVal - subclass of Mail::Field, for structured MIME fields

## SYNOPSIS

        # Create an object for a content-type field:
        $field = new Mail::Field 'Content-type';

        # Set some attributes:
        $field->param('_'        => 'text/html');
        $field->param('charset'  => 'us-ascii');
        $field->param('boundary' => '---ABC---');

        # Same:
        $field->set('_'        => 'text/html',
    		'charset'  => 'us-ascii',
    		'boundary' => '---ABC---');

        # Get an attribute, or undefined if not present:
        print "no id!"  if defined($field->param('id'));

        # Same, but use empty string for missing values:
        print "no id!"  if ($field->paramstr('id') eq '');

        # Output as string:
        print $field->stringify, "\n";

## DESCRIPTION

This is an abstract superclass of most MIME fields. It handles fields with a general syntax like this:

        Content-Type: Message/Partial;
            number=2; total=3;
            id="oc=jpbe0M2Yt4s@thumper.bellcore.com"

Comments are supported between items, like this:

        Content-Type: Message/Partial; (a comment)
            number=2  (another comment) ; (yet another comment) total=3;
            id="oc=jpbe0M2Yt4s@thumper.bellcore.com"

## PUBLIC INTERFACE

set [\%PARAMHASH | KEY=>VAL,...,KEY=>VAL]
  Instance method. Set this field. The paramhash should contain parameter names in all lowercase, with the special `"_"` parameter name signifying the "default" (unnamed) parameter for the field:

         # Set up to be...
         #
         #     Content-type: Message/Partial; number=2; total=3; id="ocj=pbe0M2"
         #
         $conttype->set('_'       => 'Message/Partial',
      		  'number'  => 2,
      		  'total'   => 3,
      		  'id'      => "ocj=pbe0M2");

  Note that a single argument is taken to be a reference to a paramhash, while multiple args are taken to be the elements of the paramhash themselves.

  Supplying undef for a hashref, or an empty set of values, effectively clears the object.

  The self object is returned.

parse_params STRING
  Class/instance utility method. Extract parameter info from a structured field, and return it as a hash reference. For example, here is a field with parameters:

          Content-Type: Message/Partial;
              number=2; total=3;
              id="oc=jpbe0M2Yt4s@thumper.bellcore.com"

  Here is how you'd extract them:

          $params = $class->parse_params('content-type');
          if ($$params{'_'} eq 'message/partial') {
              $number = $$params{'number'};
              $total  = $$params{'total'};
              $id     = $$params{'id'};
          }

  Like field names, parameter names are coerced to lowercase. The special '_' parameter means the default parameter for the field.

  NOTE: This has been provided as a public method to support backwards compatibility, but you probably shouldn't use it.

parse STRING
  Class/instance method. Parse the string into the instance. Any previous information is wiped. The self object is returned.

  May also be used as a constructor.

param PARAMNAME,[VALUE]
  Instance method. Return the given parameter, or undef if it isn't there. With argument, set the parameter to that VALUE. The PARAMNAME is case-insensitive. A "_" refers to the "default" parameter.

paramstr PARAMNAME,[VALUE]
  Instance method. Like param(): return the given parameter, or empty if it isn't there. With argument, set the parameter to that VALUE. The PARAMNAME is case-insensitive. A "_" refers to the "default" parameter.

stringify
  Instance method. Convert the field to a string, and return it.

tag
  Instance method, abstract. Return the tag for this field.