And these strings can stand standalone?
I mean, if not (if these strings are alsays suffixed to something else, e.g. page name) then, as I stated somewhere else (cannot remember where atm.), we can easily allow the @ etc. as leading characters, or even inside something given that last instance of them only will be treated specially, e.g. @Page Name will be OK, @Page Name@ will also be OK (does not match some grammar like @(\d+|L\d+(C\d+)?)$ or whatever it is, and also this could be allowed @Page Name @Wow! and @Page Name@123 will be the only one that would yield name = "@Page Name", pos = 123, and for example @Page Name@L5C10@123 would yield name = "@Page Name@L5C10", pos = 123.
Or do I miss something important here? That way many rules could be relaxed, I think, and without (much) ambiguity and with only simple rules to comprehend and to follow. 
OK, OK, I know I contradict myself a little, because I would like to see leading @ syntax for the (hopefuly) future citations. But we can still support the rest of it. After all, we can also disallow ^@L?\d as citation name (very minor issue comparing to than with the page naming).