Manual:$wgContentHandlerTextFallback

Content Models and Handlers
MediaWiki allows for page content types other than wikitext. It offers built-in support for JavaScript, CSS, JSON and plain text. Extensions can use MediaWiki's ContentHandler mechanism to add new content models for accepting different formats and controlling how they are rendered, stored and edited.
About
About the ContentHandler Content handlers and their implementation
Usage
Changing the content model of a page Changing the content model of a namespace Extensions using the ContentHandler Adding content models with an extension Examples: includes (part of Examples ) Markdown
Configuration settings
$wgContentHandlers $wgNamespaceContentModels $wgContentHandlerTextFallback $wgContentHandlerUseDB
Support and development Latest technical documentation (Git) Phabricator

Content handlers and storage: $wgContentHandlerTextFallback
How to react if a plain text version of a non-text Content object is requested using ContentHandler::getContentText()
Introduced in version:	1.21.0
Deprecated in version:	1.37.0 (Gerrit change 691704; git #e34e93f2)
Removed in version:	1.42.0 (Gerrit change 993049; git #ba1563a0)
Allowed values:	(one of the allowed parameters)
Default value:	'ignore'
Other settings: Alphabetical | By function

Allowed parameters

Depending on the value, the following action is taken when Content is not a TextContent object:

• 'ignore' - ContentHandler::getContentText() returns null
• 'fail' - Throw an MWException
• 'serialize' - Use the Content objects serialize method to get a string