code: func fieldContains(fl FieldLevel) bool {
  	field := fl.Field()
  
  	currentField, _, ok := fl.GetStructFieldOK()
  
  	if !ok {
  		return false
  	}
  
  	return strings.Contains(field.String(), currentField.String())
  }
docs: // FieldContains is the validation function for validating if the current field's value contains the field specified by the param's value.