Re: ID Characters (was: Re: 3.4. Global attributes)

I do not understand one part of this :

Jim Jewett wrote:

> Authors wishing to write robust applications are advised to use a more
> restricted set of IDs.  While "1" and $^&" are technically valid
> identifiers, they will trigger bugs in some tools.  Therefore, authors
> SHOULD stick to ID characters from the ASCII digits [0-9] and one case
> of ASCII letters (either [a-z] or [A-Z]), and SHOULD ensure that the
> first character of each ID is a letter rather than a digit.

Which tool(s) is/are likely to manifest incorrect behaviour
if an author uses mixed case for an ID ?

Philip Taylor