Hi!

Support for the TeX HTML extension from MathJax in the output of KaTeX would be nice.

Excerpt from the docs:

The HTML extension gives you access to some HTML features like styles, classes, element ID’s and clickable links. It defines the following non-standard macros:

• \class{name}{math}: Attaches the CSS class name to the output associated with math when it is included in the HTML page. This allows your CSS to style the element.
• \cssId{id}{math}: Attaches an id attribute with value id to the output associated with math when it is included in the HTML page. This allows your CSS to style the element, or your javascript to locate it on the page.