CHARSET_INFO.txt:

  New comments about ctype[].

strings/CHARSET_INFO.txt

@@ -74,7 +74,16 @@ Conversion tables
   ctype      - pointer to array[257] of "type of characters"
                bit mask for each chatacter, e.g. if a 
                character is a digit or a letter or a separator, etc.
-  to_lower   - pointer to arrat[256] used in LCASE()
+
+               Monty 2004-10-21:
+                 If you look at the macros, we use ctype[(char)+1].
+                 ctype[0] is traditionally in most ctype libraries
+                 reserved for EOF (-1). The idea is that you can use
+                 the result from fgetc() directly with ctype[]. As
+                 we have to be compatible with external ctype[] versions,
+                 it's better to do it the same way as they do...
+
+  to_lower   - pointer to array[256] used in LCASE()
   to_upper   - pointer to array[256] used in UCASE()
   sort_order - pointer to array[256] used for strings comparison