Another great post from you! It is true that to customise / develop a wiki an author does need understand quite a lot of things that TW docs themselves can’t teach you.
I’d add to your list SVG. Though often considered part of HTML it really is an image format that, to get the best from, you’ll need understand. SVG is probably the most pervasive visually important component of the TW UI.
This such a vital, simple, post I do want to comment more widely. I hope this won’t spoil your thread!
Couple of things …
1 - Teach HTML, CSS & SVG in a TW — TW is such a brilliant “dynamic” environment I do often wonder IF someone might actually write one that teaches HTML, CSS & SVG interactively. In other words TW itself as a tool to teach Web Basics?
I agree this is needed and we could build a short list into a menu like the sites menu at tiddlywiki.com for these references in a plugin you can install in your learning wiki.
It is critical we have documentation on the nexus between each of these technologies and there use in TiddlyWiki and deal with the gaps. For example how wikitext is rendered into html and html is just displayed, however CSS applies not to separate pages but to the one and same tiddlywiki page, and to do this we need to document the classes and where they are implemented in the page structure.
Regular expressions need this as well, defining it in a variable, how to build regexp for common tiddlywiki elements, in filters and searching content etc…
I do think Regular Expressions are a meat & potatoes requirement if you need interrogate one’s own wiki. It is a very interesting case in that TW natively fully supports Regular Expressions in filters.
BUT there is a double whammy to being able to fully use them in TW as: