function getMaxLength(currentInput) {
        var max = currentInput.attr('maxlength') || options.customMaxAttribute;

        if (options.customMaxAttribute && !options.allowOverMax) {
          var custom = currentInput.attr(options.customMaxAttribute);
          if (!max || custom < max) {
            max = custom;
          }
        }

        if (!max) {
          max = currentInput.attr('size');
        }
        return max;
      }
This function retrieves the maximum length of currentInput

@param currentInput
@return {number}