open_shirt currently implies shirt. However, if the former can be used for other shirt-like garments, as the wiki page says, then if one were to add it to a post with, say, a single character wearing an open lab coat, shirt would be added even though no shirt is present. Thus either the definition of open_shirt should be changed or the implication should be removed. I vote for the latter, since it would be wasteful and clunky to have "open_" tags for every kind of shirt-like garment that can be open, when people probably want them all together in searches anyway.