TheContentHandler facility is a mechanism for supporting arbitrary content types on wiki pages, instead of relying on wikitext for everything.It was developed as part of theWikidata project and is part of the MediaWiki core since version 1.21.

For the canonical overview of the ContentHandler's architecture, seeContentHandler in the MediaWiki code documentation.

For a list of available content handlers, seeContent handlers.

The rationale behind this rather radical change is that being forced to rely on wikitext for all content makes a lot of things quite cumbersome in MediaWiki.The new pluggable architecture for arbitrary types of page content will allow us to hopefully:

• use a different markup language on some or all pages, like TeX or Markdown.
• do away with special cases for CSS and JavaScript pages.
• store and edit structured configuration data in a more sensible way than e.g. what the Gadgets extension uses onMediaWiki:Gadgets-definition or the LanguageConverter onMediaWiki:Conversiontable*** pages.
• provide data "attachments" to wikitext pages, e.g. for geodata (using a "multipart" content model for the page, similar to the way email attachments are implemented using the multipart message format). (Note: this never materialized, and has now been superseded byMulti-Content Revisions.)
• transition to a system where categories etc are not maintained in the wikitext itself, while still being stored and versioned in the usual way (again, using a multipart content model).
• store structured data forWikidata easily and natively as page content.

The idea is to store other kinds of data in exactly the same way as wikitext is stored currently, but make MediaWiki aware of the type of content it is dealing with for every page.This way, any kind of data can be used as the content of a wiki page, and it would be stored and versioned exactly as before.To achieve this, the following was implemented in the MediaWiki core:

• keep track of thecontent model of every page. This is done primarily in thepage table in the database (also in therevision andarchive tables), and made accessible through the relevant core classes such asTitle,RevisionRecord, andWikiPage. Thecontent model defines thenative form of the content, be it a string containing text, a nested structure of arrays, or a PHP object. All operations on the content are performed on itsnative form.
• keep track of thecontent format (serialization format) of every revision. This is done primarily in therevision table in the database (also in thearchive table, but not in thepage table), and made accessible through the relevant core classes such asRevisionRecord. Note that the serialization format is only relevant when loading and storing the revision, no operations are performed on the serialized form of the content.
  • Note: in case of flat text content (such as wikitext), the native form of the content is the same as the serialized form (namely, a string). However, conceivably, the native form of wikitext could be some form of AST or DOM in the future.
  • Note: thepage table records the content model for the current revision, while therevision records the content model and serialization format. Model and format may in theory both change from revision to revision, though this may be confusing, and doesn't allow for meaningful diffs.

This means that all code that needs to perform any operation on the content must be aware of the content's native form.This knowledge is encapsulated using a pluggable framework of handlers, based on two classes:

• TheContent class represents the content as such, and provides an interface for all standard operations to be performed on the content's native form. It does not have any knowledge of the page or revision the content belongs to. Content objects are generally, but not necessarily, immutable.
• TheContentHandler class, representing the knowledge about the specifics of a content model without access to concrete Content. Most importantly, instances of ContentHandler act as a factory for Content objects and provide serialization/deserialization. ContentHandler objects are stateless singletons, one for each content model.

The ContentHandler is also used to generate suitable instances of subclasses ofArticle,EditPage,SlotDiffRenderer, etc.This way, a specialized UI for each content type can easily be plugged in through the ContentHandler interface.

All code that accesses the revision text in any way should be changed to use the methods provided by the Content object instead.Core classes that provide access the revision text (most importantly,RevisionRecord andWikiPage) have been adapted to provide access to the appropriate Content object instead of the text.

The assumption that pages contain wikitext is widespread through the MediaWiki code base. To remain compatible with parts of the code that still assume this, especially with extensions, is thus quite important.The right way to provide good compatibility is of course not to change public interfaces.Thus, all methods providing access to the revision content (likeRevision::getText(), etc.) remained in place, and are complemented with an alternative method that allows access to the content object instead (e.g.Revision::getContent()).The text-based methods are now deprecated, but shall function exactly as before for all pages/revisions that contain wikitext.This is also true for theaction API.

A convenience method,ContentHandler::getContentText(), is provided to make it easy to retrieve a page's text.For flat text-based content models such as wikitext (but also JS and CSS),getContentText() will just return the text, so the old text-based method will return the same as it did before for such revisions.However, in case a text-based backwards-compatible method is called on a page/revision that does not contain wikitext (or another flat text content model, such a CSS), the behavior depends on the setting of$wgContentHandlerTextFallback:ignore makes it return null,fail causes it to raise an exception, andserialize causes it to return the default serialization of the content.The default isignore, which is probably the most conservative option in most scenarios.

For editing however, non-text content is not supported per default.EditPage and the respective handlers in the action API will fail for non-textual content.

Content andContentHandler classes

• Content.php
• ContentHandler.php

Settings

• $wgContentHandlers
• $wgContentHandlerTextFallback
• $wgNamespaceContentModels

Extensions using ContentHandler

• How to add a new content model with an extension:Page content models
• Basic example:Extension:Markdown
• Category:ContentHandler extensions
• TheExamples extension
• Content handlers — a list of all content models (both in core and extensions)

• Maintained byUnknown or Unassigned^{[‍Maintainers page]}.
• Issue tracker:Phabricator MediaWiki-ContentHandler (Report an issue)

• MediaWiki development
• Data exchange with other systems
• Metadata
• ContentHandler
• Markup languages