Improve formatting.

syntax/m4.syntax

@@ -11,7 +11,7 @@
 context default
 
 	#=========================
-	# Macros with parameters
+	# Built-in macros with mandatory parameters
 	keyword whole builtin		yellow/24
 	keyword whole decr		yellow/24
 	keyword whole define		yellow/24
@@ -37,7 +37,7 @@ context default
 	keyword whole undefine		yellow/24
 
 	#=========================
-	# Macros with optional parameters
+	# Built-in macros with optional parameters
 	keyword whole changecom		yellow/24
 	keyword whole changequote	yellow/24
 	keyword whole debugfile		yellow/24