Wolfram Language & System 11.0 (2016)|Legacy Documentation
This is documentation for an earlier version of the Wolfram Language.View current documentation (Version 11.2)
gives the position of the character c in the standard alphabet in which it appears.
gives the position of c in the alphabet specified by alpha.
LetterNumber works the same with uppercase letters:
Introduced in 2015
(10.1)| Updated in 2015