When completing a word in insert mode (see |ins-completion|) from the tags file, show both the tag name and a tidied-up form of the search pattern (if there is one) as possible matches. Thus, if you have matched a C function, you can see a template for what arguments are required (coding style permitting). Note that this doesn't work well together with having "longest" in 'completeopt', because the completion from the search pattern may not match the typed text.