I would like to use Geany for editing of SVG files. But I am missing

...

some "working" filetype. I have tried "XML" and "HTML" but both are unusable.

I'm not sure what you mean. Geany SVN detected the XML filetype when I opened the example file and seemed to colour it correctly. If you're using the 0.11 release (or earlier) you can associate .svg with the XML filetype in a configuration file. (See the manual for details).

How would a SVG filetype be different from the XML filetype?

Regards, Nick

It is colored properly. But folding does not work. Why not?

markinfo