docs: add ReplacementTransformer reference

site/content/en/docs/Reference/API/Transformers/ReplacementTransformer.md

@@ -0,0 +1,64 @@
+---
+title: "ReplacementTransformer"
+linkTitle: "ReplacementTransformer"
+weight: 6
+date: 2026-07-23
+description: >
+  ReplacementTransformer copies values from a source field or literal value into target fields.
+---
+
+See [Transformers]({{< relref "../Transformers" >}}) for common required fields.
+
+`ReplacementTransformer` uses the same replacement schema as the
+[`replacements` field]({{< relref "../Kustomization%20File/replacements.md" >}})
+in a Kustomization file. Use it through the `transformers` field when the
+replacement configuration should live in a separate transformer file.
+
+* **apiVersion**: builtin
+* **kind**: ReplacementTransformer
+* **metadata** ([ObjectMeta](https://kubernetes.io/docs/reference/kubernetes-api/common-definitions/object-meta/#ObjectMeta))
+
+  Standard object's metadata.
+
+* **replacements** ([]ReplacementField)
+
+  List of replacements to apply. Each item is either an inline replacement or a
+  `path` to a file that contains a single replacement or a list of replacements.
+  An item must not set both `path` and an inline replacement.
+
+  Each inline replacement copies a value from `source` or `sourceValue` into one
+  or more `targets`. It must specify exactly one of `source` or `sourceValue`,
+  and at least one target.
+
+Example transformer file:
+
+```yaml
+apiVersion: builtin
+kind: ReplacementTransformer
+metadata:
+  name: replacement-transformer
+replacements:
+- source:
+    kind: Deployment
+    fieldPath: spec.template.spec.containers.0.image
+  targets:
+  - select:
+      kind: Deployment
+    fieldPaths:
+    - spec.template.spec.containers.1.image
+```
+
+Example Kustomization that references the transformer file:
+
+```yaml
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+- deployment.yaml
+transformers:
+- replacement-transformer.yaml
+```
+
+For the full replacement schema, field descriptions, selector behavior, and
+field path syntax, see the
+[`replacements` field documentation]({{< relref "../Kustomization%20File/replacements.md" >}}).