function number_parsePercent(percent, all) {
  switch (percent) {
    case 'center':
    case 'middle':
      percent = '50%';
      break;

    case 'left':
    case 'top':
      percent = '0%';
      break;

    case 'right':
    case 'bottom':
      percent = '100%';
      break;
  }

  if (typeof percent === 'string') {
    if (_trim(percent).match(/%$/)) {
      return parseFloat(percent) / 100 * all;
    }

    return parseFloat(percent);
  }

  return percent == null ? NaN : +percent;
}
Convert a percent string to absolute number.
Returns NaN if percent is not a valid string or number