NAME

       Mail::Field - base-class for manipulation of mail header fields

INHERITANCE

        Mail::Field is extended by
          Mail::Field::AddrList
          Mail::Field::Date
          Mail::Field::Generic

SYNOPSIS

        use Mail::Field;

        my $field = Mail::Field->new('Subject', 'some subject text');
        my $field = Mail::Field->new(Subject => 'some subject text');
        print $field->tag,": ",$field->stringify,"\n";

        my $field = Mail::Field->subject('some subject text');

DESCRIPTION

       "Mail::Field" creates and manipulates fields in MIME headers, collected within a
       Mail::Header object.  Different field types have their own sub-class (extension), defining
       additional useful accessors to the field content.

       People are invited to merge their implementation to special fields into MailTools, to
       maintain a consistent set of packages and documentation.

METHODS

   Constructors
       Mail::Field (and it's sub-classes) define several methods which return new objects. These
       can all be categorized as constructor.

       Mail::Field->combine($fields)
           Take a LIST of "Mail::Field" objects (which should all be of the same sub-class) and
           create a new object in that same class.

       Mail::Field->extract( $tag, $head [, $index ] )
           Takes as arguments the tag name, a "Mail::Head" object and optionally an index.

           If the index argument is given then "extract" will retrieve the given tag from the
           "Mail::Head" object and create a new "Mail::Field" based object.  undef will be
           returned in the field does not exist.

           If the index argument is not given the result depends on the context in which
           "extract" is called. If called in a scalar context the result will be as if "extract"
           was called with an index value of zero. If called in an array context then all tags
           will be retrieved and a list of "Mail::Field" objects will be returned.

       Mail::Field->new( $tag [, STRING | %options] )
           Create an object in the class which defines the field specified by the $tag argument.

   "Fake" constructors
       $obj->create(%options)
           This constructor is used internally with preprocessed field information.  When called
           on an existing object, its original content will get replaced.

       $obj->parse()
           Parse a field line.

   Accessors
       $obj->set(%options)
           Change the settings (the content, but then smart) of this field.

       $obj->stringify()
           Returns the field as a string.

       $obj->tag()
       Mail::Field->tag()
           Return the tag (in the correct case) for this item.  Well, actually any casing is OK,
           because the field tags are treated case-insensitive; however people have some
           preferences.

   Smart accessors
       $obj->text( [STRING] )
           Without arguments, the field is returned as stringify() does.  Otherwise, the STRING
           is parsed with parse() to replace the object's content.

           It is more clear to call either stringify() or parse() directly, because this method
           does not add additional processing.

DETAILS

   SUB-CLASS PACKAGE NAMES
       All sub-classes should be called Mail::Field::name where name is derived from the tag
       using these rules.

       •   Consider a tag as being made up of elements separated by '-'

       •   Convert all characters to lowercase except the first in each element, which should be
           uppercase.

       •   name is then created from these elements by using the first N characters from each
           element.

       •   N is calculated by using the formula :-

               int((7 + #elements) / #elements)

       •   name is then limited to a maximum of 8 characters, keeping the first 8 characters.

       For an example of this take a look at the definition of the "_header_pkg_name()"
       subroutine in "Mail::Field"

DIAGNOSTICS

       Error: Undefined subroutine <method> called
           Mail::Field objects use autoloading to compile new functionality.  Apparently, the
           method called is not implemented for the specific class of the field object.

SEE ALSO

       This module is part of the MailTools distribution, http://perl.overmeer.net/mailtools/.

AUTHORS

       The MailTools bundle was developed by Graham Barr.  Later, Mark Overmeer took over
       maintenance without commitment to further development.

       Mail::Cap by Gisle Aas <aas@oslonett.no>.  Mail::Field::AddrList by Peter Orbaek
       <poe@cit.dk>.  Mail::Mailer and Mail::Send by Tim Bunce <Tim.Bunce@ig.co.uk>.  For other
       contributors see ChangeLog.

LICENSE

       Copyrights 1995-2000 Graham Barr <gbarr@pobox.com> and 2001-2017 Mark Overmeer
       <perl@overmeer.net>.

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.  See http://www.perl.com/perl/misc/Artistic.html