%Rating=1 %Rating=3 ....
%R1,%R2,%R3...
*1,*2,*3...
I would choose a generic syntax to represent library technical info. This way leaves an opening for other requests regarding more library "tags" in the future

OK. That will need some thought, so probably best not to rush it in for the 3.6 release. Perhaps something for 3.6.1

Here's another suggestion: A button, similar to 'Clear Private Data' used by web browsers to remove the URL history, folder history, playlist entries and other stuff that XMPlay stores inside the ini file or Windows registry.
I'll add a "Clear history" button to clear the URL/folder/search history. There is also a "NoHistory" XMPLAY.INI setting that can be used (set to 1) to disable the storing of that information.