-# Note that some lexes (for example flex 2.5.4) require that there
-# be no space between -o and the output filename.
+# Note that not all lexes support -o (it is not POSIX); also
+# some lexes will only accept '-n -t', not '-nt'.
+# Also, not all makes accept $< in non-pattern rules,
+# hence the explicit filenames here.