With the renderers in 3.11 and before course formats were able to override individual methods in order to change how some parts of the course looks.

In 4.0 it is possible to override only the output classes, which is mostly useless because the DATA for the course format is always the same anyway, course formats what to change how it LOOKS (i.e. override templates).

Here is the example:

I want to modify in my course format how the button "Mark as done" looks. The template responsible for it is course/templates/completion_manual.mustache

This template is referenced by name from the template core_courseformat/local/content/cm/activity_info , and this template referenced by name from core_courseformat/local/content/cm and that one from core_courseformat/local/content/section/cmitem and that one from core_courseformat/local/content/section/cmlist and that one from core_courseformat/local/content/section and that one from core_courseformat/local/content

So it looks like I have to copy 7 templates to my course format, modify one line in each of them and also override the section_renderer::render() function because it hardcodes the 'core_courseformat/local/' prefix for templates as well