public Builder expression(@Nullable Output<String> expression) {
            $.expression = expression;
            return this;
        }
@param expression Expression represents the expression which will be evaluated by CEL. ref: https://github.com/google/cel-spec CEL expressions have access to the contents of the API request/response, organized into CEL variables as well as some other useful variables:

- &#39;object&#39; - The object from the incoming request. The value is null for DELETE requests. - &#39;oldObject&#39; - The existing object. The value is null for CREATE requests. - &#39;request&#39; - Attributes of the API request([ref](/pkg/apis/admission/types.go#AdmissionRequest)). - &#39;params&#39; - Parameter resource referred to by the policy binding being evaluated. Only populated if the policy has a ParamKind. - &#39;namespaceObject&#39; - The namespace object that the incoming object belongs to. The value is null for cluster-scoped resources. - &#39;variables&#39; - Map of composited variables, from its name to its lazily evaluated value.
  For example, a variable named &#39;foo&#39; can be accessed as &#39;variables.foo&#39;.
- &#39;authorizer&#39; - A CEL Authorizer. May be used to perform authorization checks for the principal (user or service account) of the request.
  See https://pkg.go.dev/k8s.io/apiserver/pkg/cel/library#Authz
- &#39;authorizer.requestResource&#39; - A CEL ResourceCheck constructed from the &#39;authorizer&#39; and configured with the
  request resource.

The `apiVersion`, `kind`, `metadata.name` and `metadata.generateName` are always accessible from the root of the object. No other metadata properties are accessible.

Only property names of the form `[a-zA-Z_.-/][a-zA-Z0-9_.-/]*` are accessible. Accessible property names are escaped according to the following rules when accessed in the expression: - &#39;__&#39; escapes to &#39;__underscores__&#39; - &#39;.&#39; escapes to &#39;__dot__&#39; - &#39;-&#39; escapes to &#39;__dash__&#39; - &#39;/&#39; escapes to &#39;__slash__&#39; - Property names that exactly match a CEL RESERVED keyword escape to &#39;__{keyword}__&#39;. The keywords are:
	  &#34;true&#34;, &#34;false&#34;, &#34;null&#34;, &#34;in&#34;, &#34;as&#34;, &#34;break&#34;, &#34;const&#34;, &#34;continue&#34;, &#34;else&#34;, &#34;for&#34;, &#34;function&#34;, &#34;if&#34;,
	  &#34;import&#34;, &#34;let&#34;, &#34;loop&#34;, &#34;package&#34;, &#34;namespace&#34;, &#34;return&#34;.
Examples:
  - Expression accessing a property named &#34;namespace&#34;: {&#34;Expression&#34;: &#34;object.__namespace__ &gt; 0&#34;}
  - Expression accessing a property named &#34;x-prop&#34;: {&#34;Expression&#34;: &#34;object.x__dash__prop &gt; 0&#34;}
  - Expression accessing a property named &#34;redact__d&#34;: {&#34;Expression&#34;: &#34;object.redact__underscores__d &gt; 0&#34;}

Equality on arrays with list type of &#39;set&#39; or &#39;map&#39; ignores element order, i.e. [1, 2] == [2, 1]. Concatenation on arrays with x-kubernetes-list-type use the semantics of the list type:
  - &#39;set&#39;: `X + Y` performs a union where the array positions of all elements in `X` are preserved and
    non-intersecting elements in `Y` are appended, retaining their partial order.
  - &#39;map&#39;: `X + Y` performs a merge where the array positions of all keys in `X` are preserved but the values
    are overwritten by values in `Y` when the key sets of `X` and `Y` intersect. Elements in `Y` with
    non-intersecting keys are appended, retaining their partial order.
    Required.

@return builder
sdk/java/src/main/java/com/pulumi/kubernetes/admissionregistration/v1beta1/inputs/ValidationPatchArgs.java