+&:warn [!]WARNTAG ...
+ Suppress (with !) or re-enable (without !) warnings tagged
+ WARNTAG (see section `Warnings', below). The suppression list
+ is reset at the start of processing in each subdirectory.
+ Warnings that appear at the end of processing are controlled
+ by the final warning state after processing all the toplevel
+ input files (including Final.sd.mk).
+
+&:local+global [&]VARIABLE ...
+ Suppresses the warning about seeing both VARIABLE and
+ &VARIABLE. Any & specified in the RHS is redundant: this
+ always affects both versions identically.
+
+&:changequote NEWQUOTE
+ changes the escape sequence from & to literally NEWQUOTE
+ NEWQUOTE may be any series of of non-whitespace characters,
+ and is terminated by EOL or lwsp. The whole line is
+ discarded.
+
+ After this, write NEWQUOTE instead of &, everywhere.
+ The effect is unscoped and lasts until the next setting,
+ or until the end of the current directory's Suffix.sd.mk.
+ It takes effect on &:include'd files too, so maybe set
+ it back before using &:include.
+
+ Notably
+ NEWQUOTENEWQUOTE => NEWQUOTENEWQUOTE
+ NEWQUOTE\NEWQUOTE => NEWQUOTE
+ NEWQUOTE\$ => $
+ NEWQUOTE:changequote & set escape back to &
+