&=			=>	subdir
&_			=>	subdir_
&/			=>	subdir/
&CAPS			=>	subdir_CAPS	_ counts
&lc			=>	subdir/lc	_ counts

&,= &,_ &,/ &,CAPS &,lc		prefixes $(top_srcdir)/subdir
&;= &;_ &;/ &;CAPS &;lc		prefixes $(abs_top_srcdir)/subdir

&.			=>	$(top_srcdir)
&:			=>	$(abs_top_srcdir)

& thing thing		=>	like &thing &thing (until EOL)
				(edits only `thing's which are CAPS or lc
				and follow a space)

&&			=>	&

&! spc		disables & *until* EOL

&!STUFF		STUFF is recognised instead of & (beyond EOL)
		STUFF is either all punct or all alphanum (incl _)
		any lwsp after STUFF is discarded too
eg notably
 STUFF!&		now & is recognised instead (ie back to normal)
 STUFFSTUFF	STUFF

eg
 &!@@@		@@@ is recognised instead of &
 @@@!&		go back to &

&TARGETS[_things]		is handled specially
				must be spelled precisely this way
				if no _things, means _all