I did take a quick glance through some of the extension docs, but it seems the particular subsection you discuss was not among the pages I happened to look at. I had never had occasion to use the GNU dialect in the past and searches weren't helping me find specific examples, so I appreciate you taking the time to elaborate!
Out of curiosity, which pages did you discover? Not as in "You hold it wrong.", but as in "Which pages does the unfamiliar discover.".
Are you on an OS, where using the GNU Info system is an option? I quite like it. Unfamiliar people often are deterred from using it, either, because it is in the terminal, or, because they think they are looking at a pager. When it's only the latter preventing you from using it, have in mind, that this is not in fact a simple paged document, but an interactive hypertext system, that predates the WWW. Documents are generally structured as a tree. Use the normal cursor movement, use Enter to follow links, p for previous node, n for next node, u / backspace for up/parent node, / works for text search, i searches in the index. Use info info when you want to know more. Pressing h for help also works. (I just discovered that the behaviour of h depends on your terminal size :-) .) When you look at the GNU onlinedocs, you look at a HTML version of that Info document. Using Info directly is nicer, since it has native support for jumping in the doc tree and instead of relying on an external entity (like Google) to point you to the node that contains your information (Often resulting in bringing you at another version or document entirely, which can lead to confusion.) you can use the built-in index, which is maintained by the document authors, so it will be accurate.
GNU Info is in my opinion the best and fastest way to access documentation, that is more then a simple reference sheet, when you don't object to leaving the Web browser. It even has C tutorials and all, completely offline.
IIRC I was basically doing a top-down search starting from the "Extensions to the C Language Family" [0] and the "Extensions to the C++ Language" [1] pages. I did come across the syntax/semantic extensions subpages you list, but I didn't comprehensively go through all the extensions.
> Are you on an OS, where using the GNU Info system is an option?
Technically yes, but I admittedly have basically zero experience with using it.
> Using Info directly is nicer, since it has native support for jumping in the doc tree and instead of relying on an external entity (like Google) to point you to the node that contains your information (Often resulting in bringing you at another version or document entirely, which can lead to confusion.) you can use the built-in index, which is maintained by the document authors, so it will be accurate.
I'm not entirely confident about how helpful it'd be for someone who is less familiar with the subject material like me as opposed to someone who has a general idea of what they're looking for, but I suppose I won't know until I try it.
