Hi all,

I have implemented the functionality in a form of plugin, as it was suggested by Lex.

The source code is available on Github:
https://github.com/vmkononenko/pair-tag-highlighter

I've played with several HTML files and it seems to work properly.

A bit more playing with code is needed for XML support. Quick testing showed, that in some cases it does not work.

To install plugin, run make && make install.

It may be needed to edit Makefile depending on your OS and arch.

Suggestion and bugreports are welcome. After discussion in mailing list I will follow guidelines at http://www.geany.org/manual/reference/guidelines.html regarding adding plugin to main geany-plugins repository.