For historic reasons the mobile site was built using client side templates using a templating library called Hogan.js. This caused problems with development as engineers wanting to build client side experiences using templates would have to use different template languages for desktop and mobile experiences or ship two both Mustache and Hogan to end users.

We've recently been simplifying and cleaning up the codebase, reducing technical debt [1] and as part of this effort have switched templates inside Minerva and MobileFrontend from Hogan to Mustache [2, 3] to bring them in line with the rest of the platform.

The Mustache library is smaller than Hogan and appears to be better maintained. It also has a PHP implementation which is used across MediaWiki inside cores and skins.

Longer term we are reconsidering the use of templates in our part of the tech stack but if you are developing extensions or skins that operate in an environment using a separate mobile skin you can safely and are encouraged to make use of Mustache to share code that needs to run in both PHP and JS.

[1] https://medium.com/freely-sharing-the-sum-of-all-knowledge/how-we-tackled-te... [2] https://gerrit.wikimedia.org/r/#/c/506340/ [3] https://phabricator.wikimedia.org/T220620