Hi Josef,
First of all, thanks for the answer!
I have not looked at the actual Mizar parser code for this (and do not
know it at the moment). I'd like to ask Andrzej (the chairman of Assoc. of
Mizar Users) if I can answer here public questions like this by looking at
the Mizar code (I promised not to publish it six years ago). Andrzej?
I think that the rules like this is the part of language definition (like the
overloading rules in C++, for example), and I hope that the language
defintion is open, though the pascal code for parser is closed. :)