function isLatinLetter(letter)
{
	// Combining marks are a subset of non-spacing-mark.
	if (!pL_regexp.test(letter) && !pMn_regexp.test(letter)) {
		return false
	}

	return latinLetterRegexp.test(letter)
}
Helper method to determine if a character is a Latin-script letter or not.
For our purposes, combining marks should also return true since we assume
they have been added to a preceding Latin character.