whole_func_string: function whitespace(rule, value, source, errors, options) {
    if (/^\s+$/.test(value) || value === '') {
      errors.push(util.format(options.messages.whitespace, rule.fullField));
    }
  }
func_code_string: function whitespace(rule, value, source, errors, options) {
    if (/^\s+$/.test(value) || value === '') {
      errors.push(util.format(options.messages.whitespace, rule.fullField));
    }
  }
func_documentation_string: Rule for validating whitespace.
  
  @param rule The validation rule.
  @param value The value of the field on the source object.
  @param source The source object being validated.
  @param errors An array of errors that this rule may add
  validation errors to.
  @param options The validation options.
  @param options.messages The validation messages.