} else if len(trimmedMessageExpression) != 0 {
		// use v.MessageExpression instead of trimmedMessageExpression so that
		// the compiler output shows the correct column.
		allErrors = append(allErrors, validateMessageExpression(compiler, v.MessageExpression, opts, fldPath.Child("messageExpression"))...)
	}

			},
		},
		{
			name: "messageExpression inclusion",
			input: schema.Structural{
				Generic: schema.Generic{
					Type: "string",
				},
				ValidationExtensions: schema.ValidationExtensions{
					XValidations: apiextensions.ValidationRules{
						{
							Rule:              "self.startsWith('s')",
							MessageExpression: `"scoped field should start with 's'"`,
						},
					},

  optional string reason = 3;

  // messageExpression declares a CEL expression that evaluates to the validation failure message that is returned when this rule fails.
  // Since messageExpression is used as a failure message, it must evaluate to a string.
  // If both message and messageExpression are present on a validation, then messageExpression will be used if validation fails.

	// messageExpression declares a CEL expression that evaluates to the validation failure message that is returned when this rule fails.
	// Since messageExpression is used as a failure message, it must evaluate to a string.
	// If both message and messageExpression are present on a validation, then messageExpression will be used if validation fails.

			}
			if len(rule.MessageExpression) > 0 && len(trimmedMsgExpr) == 0 {
				allErrs.SchemaErrors = append(allErrs.SchemaErrors, field.Required(fldPath.Child("x-kubernetes-validations").Index(i).Child("messageExpression"), "messageExpression must be non-empty if specified"))
			}
			if rule.Reason != nil && !supportedValidationReason.Has(string(*rule.Reason)) {