# phpman > man > Mail::Message::Head::Subset(3pm)

## NAME
    [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown) - subset of header information of a message

## INHERITANCE
     [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown) realizes a [Mail::Message::Head::Complete](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3AComplete/markdown)

     [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)
       is a [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)
       is a [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

## SYNOPSIS
     my $subset = [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)->new(...)
     $subset->isa('[Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)')  # true
     $subset->guessBodySize               # integer or undef
     $subset->isDelayed                   # true

## DESCRIPTION
    Some types of folders contain an index file which lists a few lines of information per messages.
    Especially when it is costly to read header lines, the index speeds-up access considerably. For
    instance, the subjects of all messages are often wanted, but waiting for a thousand messages of
    the folder to be read may imply a thousand network reads (IMAP) or file openings (MH)

    When you access header fields which are not in the header subset, the whole header has to be
    parsed (which may consume considerable time, depending on the type of folder).

    Extends "DESCRIPTION" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

## OVERLOADED
    Extends "OVERLOADED" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    overload: ""
        Inherited, see "OVERLOADED" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    overload: bool
        Inherited, see "OVERLOADED" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

## METHODS
    Extends "METHODS" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

### Constructors
    Extends "Constructors" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)->build( [PAIR|$field]-LIST )
        Inherited, see "Constructors" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)->new(%options)
        Inherited, see "Constructors" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

### The header
    Extends "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    $obj->isDelayed()
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->isEmpty()
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->isModified()
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->knownNames()
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->message( [$message] )
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->modified( [BOOLEAN] )
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->orderedFields()
        Inherited, see "The header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

### Access to the header
    Extends "Access to the header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    $obj->count($name)
        Count the number of fields with this $name. If the $name cannot be found, the full header
        get loaded. In case we find any $name field, it is decided we know all of them, and loading
        is not needed.

    $obj->get( $name, [$index] )
        Get the data which is related to the field with the $name. The case of the characters in
        $name does not matter. When a $name is used which is not known yet, realization will take
        place.

    $obj->study( $name, [$index] )
        Inherited, see "Access to the header" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

### About the body
    Extends "About the body" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    $obj->guessBodySize()
        The body size is defined in the "Content-Length" field. However, this field may not be
        known. In that case, a guess is made based on the known "Lines" field. When also that field
        is not known yet, "undef" is returned.

    $obj->isMultipart()
        Inherited, see "About the body" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

### Internals
    Extends "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    $obj->addNoRealize($field)
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->addOrderedFields($fields)
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->fileLocation()
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->load()
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->moveLocation($distance)
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->read($parser)
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

    $obj->setNoRealize($field)
        Inherited, see "Internals" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown)

### Error handling
    Extends "Error handling" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    $obj->AUTOLOAD()
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->addReport($object)
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->defaultTrace( [$level]|[$loglevel, $tracelevel]|[$level, $callback] )
    [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)->defaultTrace( [$level]|[$loglevel, $tracelevel]|[$level, $callback]
    )
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->errors()
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->log( [$level, [$strings]] )
    [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)->log( [$level, [$strings]] )
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->logPriority($level)
    [Mail::Message::Head::Subset](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead%3A%3ASubset/markdown)->logPriority($level)
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->logSettings()
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->notImplemented()
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->report( [$level] )
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->reportAll( [$level] )
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->trace( [$level] )
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

    $obj->warnings()
        Inherited, see "Error handling" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

### Cleanup
    Extends "Cleanup" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

    $obj->DESTROY()
        Inherited, see "Cleanup" in [Mail::Reporter](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AReporter/markdown)

## DETAILS
    Extends "DETAILS" in [Mail::Message::Head](https://www.chedong.com/phpMan.php/perldoc/Mail%3A%3AMessage%3A%3AHead/markdown).

## DIAGNOSTICS
    Error: Package $package does not implement $method.
        Fatal error: the specific package (or one of its superclasses) does not implement this
        method where it should. This message means that some other related classes do implement this
        method however the class at hand does not. Probably you should investigate this and probably
        inform the author of the package.

## SEE ALSO
    This module is part of Mail-Box distribution version 3.009, built on August 18, 2020. Website:
    <http://perl.overmeer.net/CPAN/>

## LICENSE
    Copyrights 2001-2020 by [Mark Overmeer]. For other contributors see ChangeLog.

    This program is free software; you can redistribute it and/or modify it under the same terms as
    Perl itself. See <http://dev.perl.org/licenses/>