pub(crate) fn is_letter(c: char) -> bool {
    is_lowercase_letter(c)
        || is_modifier_letter(c)
        || is_other_letter(c)
        || is_titlecase_letter(c)
        || is_uppercase_letter(c)
}
/// Return whether c has the 'Letter' Unicode property.
Return whether c has the 'Letter' Unicode property.
Return whether c has the ' Letter ' Unicode property .
pub(crate) fn is_letter(c: char) -> bool {
    is_lowercase_letter(c)
        || is_modifier_letter(c)
        || is_other_letter(c)
        || is_titlecase_letter(c)
        || is_uppercase_letter(c)
}
pub ( crate ) fn is_letter ( c : char ) -> bool { is_lowercase_letter ( c ) || is_modifier_letter ( c ) || is_other_letter ( c ) || is_titlecase_letter ( c ) || is_uppercase_letter ( c ) }
Return whether c has the 'Letter' Unicode property.
Return whether c has the ' Letter ' Unicode property .
c
char