Parsoid in PHP, or there and back again

In December 2019, we replaced the original version of Parsoid, written in JavaScript, with a version written in PHP, the primary programming language of MediaWiki. This new version, called Parsoid/PHP, is roughly twice as fast as the original JavaScript version. Parsoid/PHP brings us one step closer to integrating Parsoid and other MediaWiki wikitext-handling code into a single system.