Change 582609 had a related patch set uploaded (by DannyS712; owner: DannyS712):
[mediawiki/extensions/ChessBrowser@master] Add <fen> tags to display a single position with a static board

https://gerrit.wikimedia.org/r/582609

@Wugapodes can you take a look?

You may want to take a look at the Chess diagram template and its associated lua module (also written by @Kipod). I'm not sure how easy it is to turn lua modules into extensions, but if we want to support static, single position diagrams, it would probably be easier to start there since it already has features such as variable board sizes, fairy chess pieces, and on-board annotations like arrows.

In T248272#5993242, @Wugapodes wrote:

You may want to take a look at the Chess diagram template and its associated lua module (also written by @Kipod). I'm not sure how easy it is to turn lua modules into extensions, but if we want to support static, single position diagrams, it would probably be easier to start there since it already has features such as variable board sizes, fairy chess pieces, and on-board annotations like arrows.

For now I was just implementing a basic <fen> tag for legal positions using the existing code

Change 582609 merged by jenkins-bot:

[mediawiki/extensions/ChessBrowser@master] Add <fen> tags to display a single position with a static board

https://gerrit.wikimedia.org/r/582609