The letter-value attribute disambiguates between numbering sequences that use letters. In many languages there are two commonly
used numbering sequences that use letters. One numbering sequence assigns numeric values to letters in alphabetic sequence,
and the other assigns numeric values to each letter in some other manner traditional in that language. In English, these would
correspond to the numbering sequences specified by the format tokens a and i. In some languages, the first member of each
sequence is the same, and so the format token alone would be ambiguous. A value of alphabetic specifies the alphabetic sequence;
a value of traditional specifies the other sequence. If the letter-value attribute is not specified, then it is implementation-dependent
how any ambiguity is resolved.