In patterns, Caml Light recognizes the form
` c ` .. ` d `
(two character constants separated by ..) as a shorthand for
the pattern
where c_1, c_2, ..., c_n are the characters that occur between c and d in the ASCII character set. For instance, the pattern `0`..`9` matches all characters that are digits.`c`|`c1`|`c2`|...|`cn`|`d`