> Thanks. I should have mentioned my installation version. I already have
> a recent installation. The version I have is from 2012/01/31 (I did
> a tlmgr update --all).

Odd. Does

    \regex_replace_all:nnN { .* } { \u } \l_tmpa_tl
    \tl_show:N \l_tmpa_tl

(1) trigger an error ("regex/u-no-lbrace", probably)
(2) show "u" as the only character in \l_tmpa_tl
(3) do something else?

Does

    \def\A{foo}
    \regex_replace_all:nnN { .* } { \u{A} } \l_tmpa_tl
    \tl_show:N \l_tmpa_tl

correctly set \l_tmpa_tl to "foo"?

Regards,
Bruno