Here is the current wiki for the [diagrams] tag:
{diagrams} is for general questions about vector graphics created programmatically inside a (La)TeX document. For questions about specific packages, use the appropriate tag, e.g. {tikz-pgf} or {pstricks}. For questions about inclusion of external graphic files, use {graphics} instead.
This wiki does not specify whether a tag such as tikz-pgf should be used in addition to the diagrams tag, or instead of it.
Based on the results of this question, the community consensus seems to be that it is often acceptable to post, e.g., a pstricks answer to a tikz question for the benefit of the community, even if such an answer is less useful to the OP. As an extension of this policy, it seems to me that a question that is likely to attract answers using more than one drawing program ought to have the diagrams tag added in addition to a more specific tag such as tikz-pgf.
If this tagging policy were followed, it would, potentially, make it slightly easier to search for questions on a specific type of drawing problem (e.g., how to draw nested spheres). However, a much bigger effect is that it would be easier for someone who likes to provide pstricks, MetaPost, or Asymptote answers to (say) tikz questions, since the diagrams tag would help to identify the fraction of tikz questions general enough for this to make sense. (Full disclosure: I have been known to provide Asymptote answers to TikZ questions.) Depending on the views of the community, this could be seen as either a positive or a negative thing.
Thus, the question: If a question about a drawing package is general enough that an answer using a different drawing package could be beneficial to the community, should that question be given the diagrams tag in addition to a package-specific tag?
The ultimate goal of this question is to improve the diagrams tag wiki to clarify this issue.
