Right now we have two questions tagged tikz-chains. I was first going to post yet another tagging meta question, but I thought I would be bold and say we do not need a tag for individual TikZ libraries. I would suspect that TikZ experts can answer questions about tikz-chains, and vice versa.
I can't suggest the merge since I don't have a high enough score in the tag to do so (you need a 5 in tag to be merged; my bronze tikz-pgf medal is no good!)
I suggest renaming tikz-chains into chains, for questions about chains in general, such as markow chains and similar diagrams, done with pgf, TikZ, PSTricks, amscd, xy-pic or any other drawing tool. Tags tikz-pgf and chains are a good tag pair on a question, better than tikz-pgf on its own.
We already have got 328 tikz-pgf questions after some months, I think it's good to have tags for being able to filter. If I would work on a problem with chains, I would be thankful to have such a tag for easy browsing collected questions about chains.
Chains mean a special kind of diagrams, but I don't have a problem with it. They are outstanding, as the existence of the Tikz chains library indicates.
