Hi all, I wanted to use `mailcap-view-file' in some package (mu4e) in order to view some attachment using some appropriate viewer. I've tested with some pdf attachment which triggered an error because I use pdf-tools which adds an entry to `mailcap-mime-data' where the viewer is the symbol `pdf-view-mode' (a major-mode) whereas `mailcap-view-file' currently only handles the "viewer is a string naming some executable" case. The default value of `mailcap-mime-data' has tons of viewers being major-mode symbols, so that can't be wrong. It's docstring also says: Where VIEWERINFO specifies how the content-type is viewed. Can be a string, in which case it is run through a shell, with appropriate parameters, or a symbol, in which case the symbol is ‘funcall’ed if and only if it exists as a function, with the buffer as an argument. Well, that's strange. All symbol-valued VIEWERINFOs are functions of zero args, mostly major-modes. They can't get the buffer (which buffer?!) as an argument. So I propose the attached patch which teaches `mailcap-view-file' the symbol/function-valued viewer case and adjust the docs to match what's already there.