code: func (v *Validate) RegisterValidation(tag string, fn Func) error {
  	return v.RegisterValidationCtx(tag, wrapFunc(fn))
  }
docs: // RegisterValidation adds a validation with the given tag
  //
  // NOTES:
  // - if the key already exists, the previous validation function will be replaced.
  // - this method is not thread-safe it is intended that these all be registered prior to any validation