Regex Spanish VAT number (NIF, CIF, NIE)

The Spanish VAT number is the taxpayer's NIF preceded by 'ES': 9 characters where the first, the last, or both are letters. The Commission's VIES FAQ describes it as: 'the first and last characters may be alpha or numeric, but they may not both be numeric'. In practice a company has a CIF (letter, 7 digits, a digit or letter check), an individual a DNI (8 digits and a letter) or a NIE (X, Y or Z, 7 digits, a letter). The attempts read disagree: the published validator.js version rejects CIFs with a digit check and accepts '_' in front, its development version rejects individuals, valvat and jsvat accept any leading letter (I and O included), and the Regular Expressions Cookbook's regex accepts nine digits. Here's a pattern following the Commission's rule and excluding the letters I, O and T up front, compared against those attempts.