PHP. Руководство по PHP. 2005
ctype_alpha
ctype_alpha
Описание
bool ctype_alpha (string text)Checks if all of the characters in the provided string, text, are alphabetic. In the standard C locale letters are just [A-Za-z] and ctype_alpha() is equivalent to (ctype_upper($text) || ctype_lower($text)) if $text is just a single character, but other languages have letters that are considered neither upper nor lower case.