Meta data

Additional data, Foswiki-generated or from forms, may be embedded in the topic text using META: macros

Overview

The default store engines store topics in plain-text files on disk, in a simple and obvious directory structure. The big advantage of this approach is that it makes it very easy to manipulate topics from outside Foswiki, and it is also very robust; there are no complex binary indexes to maintain, and moving a topic from one installation to another is as simple as copying a couple of text files.

To keep everything together in one place, meta-data (Foswiki-generated or from forms) is embedded directly in topics, using special macros. These macros are easy to spot, as they all start with the reserved META: prefix.

META: data includes information such as file attachments, topic movement history, and form field values. For efficiency reasons, the topic history is not stored in this meta-data, but is expected to be implemented elsewhere by the store engine.

Meta data syntax

• Format is the same as for any other macros except that each meta-data macro must be on a line on its own.
  • %META:<type>{key1="value1" key2="value2" ...}%
• The characters %"\r\n{} are encoded in argument values, using the standard URL encoding.
• Meta-data is divided into core meta-data, described below, and extension meta-data, which shares the same syntax but is used by extensions.
• Dates are stored as "epoch times" i.e. the integer number of seconds since 1st January 1970.

Example of core meta-data

%META:TOPICINFO{version="6" date="1655468868" author="LastEditor" format="1.0"}%
   text of the topic
%META:TOPICMOVED{from="Real.SecretAgents" to="Hollywood.SecretAgents"
   by="CoverUp" date="1655468868"}%
%META:TOPICPARENT{name="MilitaryIntelligence5"}%
%META:FILEATTACHMENT{name="CV.txt" version="3" ... }%
%META:FILEATTACHMENT{name="Photo.gif" version="1" ... }%
%META:FORM{name="SecretAgentForm"}%
%META:FIELD{name="ChosenWeapon" value="Beretta"}%
%META:FIELD{name="Paramour" value="PussyGalore"}%
%META:PREFERENCE{name="ALLOWTOPICCHANGE" value="JamesBond"}%
%META:PREFERENCE{name="DENYTOPICVIEW" value="ErnstBlofeld"}%

Core meta-data

The following meta-data macros are supported by the Foswiki core. Other macros may be used by extensions; see the extension documentation for more details. The core will read and write these extension macros, but will otherwise ignore them.

Some fields are required by macros, while others are optional. Required fields are marked with a ® symbol. The ® character is not part of the attribute name.

META:TOPICINFO

This macro caches some of the information that would normally be derived from the underlying store engine. It does this for efficiency reasons.

Key	Comment
author®	Canonical user identifier of last user to change the topic. The exact format of this depends on the user mapping manager.
version	Topic version; a plain integer.
date	epoch time
format	Format of this topic, will be used for automatic format conversion
reprev	Set when a revision is overwritten by the same author within the {ReplaceIfEditedAgainWithin} window (set in configure ). If reprev is the same as version, it prevents Foswiki from attempting to do a 3-way merge when merging overlapping edits by two different users.

Note that the version and date fields are advisory only and cannot be trusted. This is because processes outside of Foswiki's control may write topic files without maintaining these fields.

META:TOPICMOVED

This only exists if the topic has been moved. If a topic is moved more than once, only the most recent META:TOPICMOVED meta datum exists in the topic. Older ones can to be found in the topic history.

%META:TOPICMOVED{from="Real.SecretAgents" to="Hollywood.SecretAgents" by="CoverUp" date="1416592876"}%

Key	Comment
from®	Full name, i.e., web.topic
to®	Full name, i.e., web.topic
by®	Canonical user identifier of who moved the topic. The exact format of this depends on the user mapping manager.
date®	epoch time

Notes:

• the moved version numbers can be deduced from the topic history.

META:TOPICPARENT

The topic from which this topic was created, typically when clicking on a ? question mark link, or by filling out a form. The topic parent may also be manipulated in the user interface.

Key	Comment
name®	Normally just TopicName, but it can be a full Web.TopicName format if the parent is in a different Web.

META:FILEATTACHMENT

Reference to a file attached to this topic.

Key	Comment
name®	Name of file, no path. Must be unique within topic
version	An integer
path	Full path file was loaded from
size	In bytes
date	epoch time when the file was attached
user	Canonical user identifier of user who uploaded the attachment. The exact format of this depends on the user mapping manager.
comment	As supplied when file uploaded
attr	h if hidden, optional

Extra fields that are added if an attachment is moved:

Key	Comment
movedfrom	full topic name - web.topic.filename
movedby	Canonical user identifier of user who moved the attachment. The exact format of this depends on the user mapping manager.
movedto	full topic name - web.topic.filename
movedwhen	epoch time

META:FORM

Key	Comment
name®	The name of the topic containing the form definition. Can optionally include the web name (i.e., web.topic), but doesn't normally

META:FIELD

Should only be present if there is a META:FORM entry.

Key	Name
name®	Ties to entry in the form definition. This is the title with all characters except alphanumerics and . removed
value®	Value user has supplied via form
title	Full text from the form definition

META:PREFERENCE

Out-of-band preference.

Key	Name
name®	Preference name
value®	Preference value
type	Set or Local (Set is the default)

Recommended sequence

There is no absolute need for meta-data macros to be listed in a specific order within a topic, but it makes sense to do so, because form fields are displayed in the order they are defined when the topic is viewed.

The recommended sequence is:

• META:TOPICINFO
• META:TOPICPARENT (optional)
• text of topic
• META:TOPICMOVED (optional)
• META:FILEATTACHMENT (0 or more entries)
• META:FORM (optional)
• META:FIELD (0 or more entries; FORM required)
• META:PREFERENCE (0 or more entries)

Viewing meta-data embedded in page source

You can append the raw=debug parameter to the URL to view the topic text with embedded meta-data, e.g: debug view for this topic. raw=all lets you view the topic source as plain text, e.g: plain text view for this topic.

Including meta data in viewed topics

%META

Meta-data belonging to the viewed topic can be included in the view using the %META macro. See VarMETA for details.

%FORMFIELD

The %FORMFIELD macro lets you inspect the values of form field meta-data in other topics. See VarFORMFIELD for details.

%SEARCH

%SEARCH can also be used to extract meta data. See VarSEARCH and the examples in FormattedSearch and SearchPatternCookbook.

Extending meta-data in Extensions

Extensions can extend meta-data with information of their own. See Foswiki::Func for more information.

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Related Topics: DeveloperDocumentationCategory