Hello all,
The \tl_tail:w function is deprecated and will be removed from expl3
after 2012-12-31.
The background here is that as implemented in the current release,
\tl_tail:n will strip the braces in output such as
\tl_tail:n { a { b } }
but not
\tl_tail:n { a { b } { c } }
An upcoming CTAN release will fix the behaviour of \tl_tail:n such that
braces will never be removed (the 'tail' will be 'what is left after
\tl_head:n has acted'). However, this cannot be fixed in \tl_tail:w, and
so we are removing it as documented.
The recommended replacement is
\use_none:n <tokens to have head removed>
with either inside a \tl_if_blank:nF test or the use of an empty group
\use_none:nn <tokens to have head removed> { }
Also note that \tl_tail:n will prevent expansion of the result inside a
x-type expansion
\tl_set:Nx { \tl_tail:n { <tokens> } }
and expands correctly inside an f-type expansion
\tl_set:Nf { \tl_tail:n { <tokens> } }
and so the functionality of \tl_tail:w is very rarely required.
--
Joseph Wright