On 10/02/2010 14:52, Heiko Oberdiek wrote:
> If an expandable version is not an issue, then \pdfstrcmp
> can be implemented in virgin TeX. If the input of \pdfstrcmp
> consists of `other' and perhaps `space' tokens, then
> even an expandable version can be simulated. The main problem
> is AFAIK the conversion of a general token list to the string
> representation in an expandable way (that means without
> having \edef).

What happens at present is more or less that: \tl_if_eq:nn(TF) uses 
\pdfstrcmp if available and a non-expandable version otherwise.
Joseph Wright