Only highlight keywords accessible to the sketch

keywords.txt files in libraries should highlight only if the library they exist is included in the sketch.. It's frustrating to see the highlights of every library you have installed, even when you are not using it. Especially if you have installed so many libraries!

Start by tracing how the IDE loads library keywords and determines which libraries are included in a sketch. Confirm the current highlighting behavior with a sketch that uses one installed library alongside other installed libraries; done means only keywords from libraries accessible to that sketch are highlighted.

Written by the indexing model from the issue text.