MessageExpression: `self + " `,
								},
							},
						},
					},
				},
			},
			expectedErrors: []validationMatch{
				invalid("spec.validation.openAPIV3Schema.properties[f].x-kubernetes-validations[0].messageExpression"),
			},
		},
		{
			name: "x-kubernetes-validations rule invalidated by messageExpression not returning a string",

						},
					},
					"messageExpression": {
						SchemaProps: spec.SchemaProps{

		copy(dAtA[i:], *m.Reason)
		i = encodeVarintGenerated(dAtA, i, uint64(len(*m.Reason)))
		i--
		dAtA[i] = 0x22
	}
	i -= len(m.MessageExpression)
	copy(dAtA[i:], m.MessageExpression)
	i = encodeVarintGenerated(dAtA, i, uint64(len(m.MessageExpression)))
	i--
	dAtA[i] = 0x1a
	i -= len(m.Message)
	copy(dAtA[i:], m.Message)
	i = encodeVarintGenerated(dAtA, i, uint64(len(m.Message)))
	i--

		copy(dAtA[i:], *m.Reason)
		i = encodeVarintGenerated(dAtA, i, uint64(len(*m.Reason)))
		i--
		dAtA[i] = 0x22
	}
	i -= len(m.MessageExpression)
	copy(dAtA[i:], m.MessageExpression)
	i = encodeVarintGenerated(dAtA, i, uint64(len(m.MessageExpression)))
	i--
	dAtA[i] = 0x1a
	i -= len(m.Message)
	copy(dAtA[i:], m.Message)
	i = encodeVarintGenerated(dAtA, i, uint64(len(m.Message)))
	i--

            "type": "string"
          },
          "messageExpression": {

- Added `messageExpression` field to `ValidationRule`. ([#115969](https://github.com/kubernetes/kubernetes/pull/115969), [@DangerOnTheRanger](https://github.com/DangerOnTheRanger))

### Feature

- A ValidatingAdmissionPolicy now has its `messageExpression` field checked against resolved types. ([#119209](https://github.com/kubernetes/kubernetes/pull/119209), [@jiahuif](https://github.com/jiahuif)) [SIG API Machinery]