---
name: "Mail::Message::Head::Subset"
section: "3pm"
platform: "linux"
package: "perl-mail-box"
version: "4.02-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Mail::Message::Head::Subset"
---

# Mail::Message::Head::Subset(3pm)

subset of header information of a message

## NAME

Mail::Message::Head::Subset - subset of header information of a message

## INHERITANCE

```
 Mail::Message::Head::Subset realizes a Mail::Message::Head::Complete
 Mail::Message::Head::Subset
   is a Mail::Message::Head
   is a Mail::Reporter
```

## SYNOPSIS

```
  my $subset = Mail::Message::Head::Subset->new(...)
  $subset->isa('Mail::Message::Head')  # 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.

## OVERLOADED

Extends "OVERLOADED" in Mail::Message::Head.

- overload: **""** stringifaction

  Inherited, see "OVERLOADED" in Mail::Message::Head

- overload: **bool** true/false

  Inherited, see "OVERLOADED" in Mail::Message::Head

## METHODS

Extends "METHODS" in Mail::Message::Head.

### Constructors

Extends "Constructors" in Mail::Message::Head.

- $class-\>**build**( \[PAIR\|$field\]-LIST )

  Inherited, see "Constructors" in Mail::Message::Head

- $class-\>**new**(%options)

  Inherited, see "Constructors" in Mail::Message::Head

### Attributes

Extends "Attributes" in Mail::Message::Head.

### The header

Extends "The header" in Mail::Message::Head.

- $obj-\>**isDelayed**()

  Inherited, see "The header" in Mail::Message::Head

- $obj-\>**isEmpty**()

  Inherited, see "The header" in Mail::Message::Head

- $obj-\>**isModified**()

  Inherited, see "The header" in Mail::Message::Head

- $obj-\>**knownNames**()

  Inherited, see "The header" in Mail::Message::Head

- $obj-\>**message**( \[$message\] )

  Inherited, see "The header" in Mail::Message::Head

- $obj-\>**modified**( \[BOOLEAN\] )

  Inherited, see "The header" in Mail::Message::Head

- $obj-\>**orderedFields**()

  Inherited, see "The header" in Mail::Message::Head

### Access to the header

Extends "Access to the header" in Mail::Message::Head.

- $obj-\>**count**($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. Improves base, see "Access to the header" in Mail::Message::Head

- $obj-\>**study**( $name, \[$index\] )

  Inherited, see "Access to the header" in Mail::Message::Head

### About the body

Extends "About the body" in Mail::Message::Head.

- $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. Improves base, see "About the body" in Mail::Message::Head

- $obj-\>**isMultipart**()

  Inherited, see "About the body" in Mail::Message::Head

### Internals

Extends "Internals" in Mail::Message::Head.

- $obj-\>**addNoRealize**($field)

  Inherited, see "Internals" in Mail::Message::Head

- $obj-\>**addOrderedFields**($fields)

  Inherited, see "Internals" in Mail::Message::Head

- $obj-\>**fileLocation**()

  Inherited, see "Internals" in Mail::Message::Head

- $obj-\>**load**()

  Inherited, see "Internals" in Mail::Message::Head

- $obj-\>**moveLocation**($distance)

  Inherited, see "Internals" in Mail::Message::Head

- $obj-\>**read**($parser)

  Inherited, see "Internals" in Mail::Message::Head

- $obj-\>**setNoRealize**($field)

  Inherited, see "Internals" in Mail::Message::Head

### Error handling

Extends "Error handling" in Mail::Message::Head.

- $obj-\>**AUTOLOAD**()

  Inherited, see "Error handling" in Mail::Reporter

- $obj-\>**notImplemented**()

  Inherited, see "Error handling" in Mail::Reporter

### Cleanup

Extends "Cleanup" in Mail::Message::Head.

- $obj-\>**DESTROY**()

  Inherited, see "Cleanup" in Mail::Reporter

## DETAILS

Extends "DETAILS" in Mail::Message::Head.

## DIAGNOSTICS

- Error: class $package does not implement method $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. Cast by `notImplemented()`

## SEE ALSO

This module is part of Mail-Box version 4.02, built on April 10, 2026. Website: *http://perl.overmeer.net/CPAN/*

## LICENSE

For contributors see file ChangeLog.

This software is copyright (c) 2001-2026 by Mark Overmeer.

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