Letter
['A' + 1 ... 'D' + 1] = Letter | Hex,
['E' + 1] = Letter | Hex | Exp, /* E<exp> */
['F' + 1] = Letter | Hex,
['G' + 1 ... 'O' + 1] = Letter,
['P' + 1] = Letter | Exp, /* P<exp> */
['Q' + 1 ... 'Z' + 1] = Letter,
['a' + 1 ... 'd' + 1] = Letter | Hex,
['e' + 1] = Letter | Hex | Exp, /* e<exp> */
['f' + 1] = Letter | Hex,
['g' + 1 ... 'o' + 1] = Letter,
['p' + 1] = Letter | Exp, /* p<exp> */
['q' + 1 ... 'z' + 1] = Letter,
['_' + 1] = Letter,
if (!(class & (Dot | Digit | Letter)))
if (!(cclass[next + 1] & (Letter | Digit)))
if (class & Letter)