&^ => $(top_srcdir)/subdir or $(top_srcdir)
&~ => $(abs_top_srcdir)/subdir or $(abs_top_srcdir)
-&& => &
+&& => &&
+\& => &
& thing thing... & => each thing prefixed by &/ &^ &~ resp
& ^ thing thing... & each thing is any non-ws
& ~ thing thing... & & may be omitted before EOL or before \EOL
+ other &'s not recognised
CAPS is [A-Z][0-9_A-Z]*(?!\w)
lc is [a-z][-+,0-9_a-z]*(?!\w)
-&! spc disables & *until* EOL
+&!<spaces or tabs> disables & *until* EOL (and disappears)
&!STUFF STUFF is recognised instead of & (beyond EOL)
- STUFF is either all punct or all alphanum (incl _)
+ STUFF is either all ASCII punct or all ASCII alphanum (incl _)
any lwsp after STUFF is discarded too
+
eg notably
STUFF!& now & is recognised instead (ie back to normal)
STUFFSTUFF STUFF