Parsoid in PHP, or There and Back Again

In December 2019, we replaced the original version of Parsoid, written in the JavaScript programming language, with a version written in PHP, which is the primary programming language of MediaWiki. This new version, which we call Parsoid/PHP, is roughly twice as fast on most requests as the original version (retroactively renamed Parsoid/JS). Parsoid/PHP also brings us one step closer to integrating Parsoid and other MediaWiki wikitext-handling code into a single system, which will be easier to maintain and extend.