This makes CodeMirror (https://codemirror.net/) available as a text editor. It provides syntax highlighting, autocompletion, etc. for HTML, JS and CSS (maybe in future, more languages will be supported here).

It is especially useful in all places where you can't use the embedded CodeMirror instance in TinyMCE source code view (because of filtering), e.g. * for mod_data template editing * for creating templates for tiny_elements