&!<spaces or tabs> disables & *until* EOL (and disappears)
-&!STUFF STUFF is recognised instead of & (beyond EOL)
- STUFF is either all ASCII punct or all ASCII alphanum (incl _)
- any lwsp after STUFF is discarded too
+&!STUFF<lwsp> STUFF is recognised instead of &
+ the terminating lwsp is discarded too
+ may also occur at eol
eg notably
STUFF!& now & is recognised instead (ie back to normal)