And for those who need less than Helma NG, this article might be helpful.
Update: I was wrong about template inheritance, Helma NG does support it, via the "extends" tag. And the development branch has now also appengine persistence support (demo).
While the basic features of the codemirror syntaxengine now are part of bespin (and that is just syntax highlighting), I started today to experiment to add an advanced feature: Auto indenting of current line or a selection based on lexical analysis. The user just has to press CTRL + TAB (but could be any other key binding of course). The information about what codemirror thinks is the correct indentation is already internally stored for each line of the source document, all I had to do was to add some code which inserts or deletes some whitespace at the begin of those lines the user marked for auto-indentation. That is at least what I thought. Unfortunately it doesn't work yet reliable (and that is my fault, because the original codemirror editor does perfectly auto-indent) and also is not yet integrated into bespins undo/redo system, so it needs another iteration, before I can submit a patch, but if anybody wants to help working on it, take a look at the auto-indent code I added.
Geek and freelance web developer. Other interests: Photography, running, drinking coffee and foreign languages (Portuguese, Italian, French and Spanish. German is my native language).