NOTES

   1 &=                      =>      subdir
   2 &_                      =>      subdir_
   3 &/                      =>      subdir/
   4 &CAPS                   =>      subdir_CAPS     _ counts
   5 &lc                     =>      subdir/lc       _ counts
   6
   7 &,= &,_ &,/ &,CAPS &,lc         prefixes $(top_srcdir)/subdir
   8 &;= &;_ &;/ &;CAPS &;lc         prefixes $(abs_top_srcdir)/subdir
   9
  10 &.                      =>      $(top_srcdir)
  11 &:                      =>      $(abs_top_srcdir)
  12
  13 & thing thing           =>      like &thing &thing (until EOL)
  14                                 (edits only `thing's which are CAPS or lc
  15                                 and follow a space)
  16
  17 &&                      =>      &
  18
  19 &! spc          disables & *until* EOL
  20
  21 &!STUFF         STUFF is recognised instead of & (beyond EOL)
  22                 STUFF is either all punct or all alphanum (incl _)
  23                 any lwsp after STUFF is discarded too
  24 eg notably
  25  STUFF!&                now & is recognised instead (ie back to normal)
  26  STUFFSTUFF     STUFF
  27
  28 eg
  29  &!@@@          @@@ is recognised instead of &
  30  @@@!&          go back to &
  31
  32 &TARGETS[_things]               is handled specially
  33                                 must be spelled precisely this way
  34                                 if no _things, means _all