LetterQ

LetterQ(expr)

tests whether expr is a string, which only contains letters.

A character is considered to be a letter if its general category type, provided by the Java method Character#getType() is any of the following:

• UPPERCASE_LETTER
• LOWERCASE_LETTER
• TITLECASE_LETTER
• MODIFIER_LETTER
• OTHER_LETTER

Not all letters have case. Many characters are letters but are neither uppercase nor lowercase nor titlecase.