[XeTeX] Command \providelength already defined

[Philip Taylor]

Herbert Schulz wrote:

> It may be that polyglossia is more careful about re-defining commands.

I don't speak LaTeX, Herb, but I would be interested to know if in
addition to \newcommand, \renewcommand, etc., there is something along
the lines of

	\defineunlessincompatible <command><parameter list><expansion>

that would check to see if <command> is already defined, if so, compare
its parameter list and expansion with those specified, and warn if
either or both differ, and otherwise silently define <command> as
specified ?

** Phil.