Parsoid/Parser Unification/Media structure/FAQ

What do you mean by media structure?
When files are included in a page (example: ), MediaWiki's parser outputs some HTML that represents that media for your browser to render – the instructions for the browser so it be correctly shown on your screen. The choice of HTML tags and attributes, and how they are arranged to form a DOM tree, are the structure we're considering.

What can be improved about the current structure?
The current structure is composed of nested div tags and class attributes, which don't convey much meaning. The markup is irregular, making it harder to query and style. And the output differs from that of other products, like the VisualEditor / Parsoid combo. See the RFC for the finer details. The output for the example above looks like this currently:

What are you replacing it with?
The structure we're replacing it with is composed of semantic markup, which will provide accessibility benefits. The markup will be more regular and specified, making it easier and more efficient to query and style. Moreover, using the same structure that has been piloted in Parsoid will provide consistency between products and reduce some CSS redundancy. The output for the example above will look like this:

Why are you doing this now?
A medium term goal of the Content Transform Team at the WMF is to replace MediaWiki's legacy parser with Parsoid, a bidirectional wikitext to HTML5 parser. In order to get there, the legacy parser and Parsoid need to produce compatible HTML. Parsoid has been generating this new media structure for quite some time, to good effect. In order to lessen the disruption of changing parsers all at once, we're rolling out an isolated piece in preparation for further changes to come.

How has this been tested?

 * 1) The new structure has been piloted in Parsoid which is used in several active products like Visual Editor and the mobile apps. As editors and readers used these products, they flagged rendering differences with the old structure and problems with the new structure which we've fixed those over the years.
 * 2) In addition, we've done several rounds of visual difference testing where thousands of pages are rendered with the old and new structure and the rendering compared at a pixel level.
 * 3) We've also already deployed this change to several wikis, including mediawiki.org, wikitech, and all the group 0 wikis.

What's left to do?

 * 1) Code that interacts with the page, like JavaScript for extensions, user scripts and gadgets will need to be adjusted to the new structure, hopefully in a forwards and backwards compatible way.
 * 2) Skins will need to ask for the "content-media" feature or provide their own styling, since classes targeting the old structure won't apply.
 * 3) Some wikis have CSS in MediaWiki:Commons.css that will need to be ported to the new structure.

How can I help?
Test your code on the wikis we've deployed to and file tasks with the  tag.

When will you be rolling this out?
As above, it's already live on several wikis. However, we won't continue to push forward until the known issues are addressed and we've done some level of auditing of user scripts and gadgets to ensure we're causing as little disruption to readers and editors as possible.

The "image" class is no longer present on file description links
By default, a file (ex. ) will link to its description page and would previously be given a. In contrast, an explicit link (ex. ) would not result in that class being applied. In the new structure, the class serving the same purpose has been renamed to. Selectors should target the new class, where appropriate. For example, see https://www.mediawiki.org/w/index.php?title=Snippets%2FDirect_imagelinks_to_Commons&type=revision&diff=5451422&oldid=3976429

The media option is now applied to the wrapper
Previously, the class media option (ex.  ) would be applied to the media element. In order to allow the most flexibility when selecting within the structure, the class has been moved to the outer wrapper.