static alpha2number(alpha) {
    let result = 0;
    const alphalength = XTableUtils.alphachars.length;
    for (let i = 0, l = alpha.length; i < l; i += 1) {
      if (i > 0) {
        result += 1;
      }
      const current = XTableUtils.alphaIndex(alpha[i]);
      if (current === -1) {
        throw new Error('Invalid alpha');
      }
      result = result * alphalength + current;
    }
    return result;
  }
Converts an alpha from excel to its number equivalent.
@param {String} alpha Alpha representation, example: 'AB'. Is the format
                      for naming columns in Excel.
@returns {Number} Alpha in number format.