Hello,
I thought that @U{....} was accepted in 'contain_plain_text' @-commands,
but I checked the code and tested and found out that it is not the case
(while answering Werner on @sortas). I think that it should be. I
would also argue that @inlineifclear and @inlineifset could also be
there. @w could also have been in @sortas, but this context is also
for the accent command argument, in which there should not be @w.-- Pat
