subdirmk: warning (unknown-warning): ./Prefix.sd.mk:7: unknown warning many-requests-for-unknown-warning requested
subdirmk: warning (single-char-var): ./Dir.sd.mk:8: possibly confusing unbracketed single-char $-expansion
subdirmk: warning (broken-var-ref): ./Dir.sd.mk:19: broken $&... expansion; you probably meant &$
subdirmk: warning (local+global): saw both NOWARN1 and &NOWARN1
 saw NOWARN1 at ./sub/dir/Dir.sd.mk:24
 saw &NOWARN1 at ./Dir.sd.mk:14
 expectedly saw NOWARN1 at ./Dir.sd.mk:14
subdirmk: warning (local+global): saw both WARN and &WARN
 saw WARN at ./Dir.sd.mk:6
 saw WARN at ./Dir.sd.mk:9
 saw WARN at ./sub/dir/Dir.sd.mk:19
 saw WARN at ./sub/dir/Dir.sd.mk:22
 saw &WARN at ./Dir.sd.mk:7
 saw &WARN at ./Dir.sd.mk:10
 saw &WARN at ./Dir.sd.mk:11
 saw &WARN at ./sub/dir/Dir.sd.mk:18
 saw &WARN at ./sub/dir/Dir.sd.mk:27
 expectedly saw &WARN at ./sub/dir/Dir.sd.mk:21
subdirmk: warning (unknown-warning): ./sub/dir/Dir.sd.mk:6: attempt to suppress unknown warning(s) `some-unknown-warning'