Best practise to deal with incompatible usage of intergerp

Hi Aidian, Stephen,

I find, in nxml code integerp is used to determind if its argument is a
single character.

To make the code work I changed this kind of intergerp call to characterp.
Anyway nxml still mix use of character and integer type in someother logic.
such as #'xsdre-range-list-to-char-alternative which will result a C level
argument validation error of intergerp.

My question is: how was this kind of incompatible usage of integerp usage
handled in the past? Are there any good practice to follow?

Would you mind tell the history of intergerp change if possiable? When was
it change to be incompatible with FSF's one? and why.

Thanks,
Kai