Metadata Matches Regex in CEL expressions

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: metadata-match-regex
  annotations:
    policies.kyverno.io/title: Metadata Matches Regex in CEL expressions
    policies.kyverno.io/category: Other in CEL
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: Pod, Label
    policies.kyverno.io/minversion: 1.11.0
    kyverno.io/kubernetes-version: 1.26-1.27
    policies.kyverno.io/description: Rather than a simple check to see if given metadata such as labels and annotations are present, in some cases they need to be present and the values match a specified regular expression. This policy illustrates how to ensure a label with key `corp.org/version` is both present and matches a given regex, in this case ensuring semver is met.
spec:
  validationFailureAction: Audit
  background: false
  rules:
    - name: check-for-regex
      match:
        any:
          - resources:
              kinds:
                - Pod
              operations:
                - CREATE
                - UPDATE
      validate:
        cel:
          expressions:
            - expression: object.metadata.?labels[?'corp.org/version'].orValue('default').matches('^v[0-9].[0-9].[0-9]$')
              message: "The label `corp.org/version` is required and must match the specified regex: ^v[0-9].[0-9].[0-9]$"