While on the colspec= issue ... I would recommend elimination of the
upper case requirement on the alignment prefix characters. The fact that
some fonts for computer usage are so poorly designed that it is difficult
or impossible to differentiate 1/L and 0/o seems poor justification
for making entry of the values more cumbersome. Leaving the values case
insensitive will be less confusing and would also be the no suprises
expected behavior. Users with difficulty distinguishing 1/L can use
upper case and it will work. In the mean time the rendering rule
re. ignoring what isn't understood won't cause difficulty for the rest
of us.
David Morris