Vendor-Extensions.md

+## Here is a list of [vendor extensions](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#specification-extensions) used by different generators.
+
+The list may not be up-to-date so the best way is to look for "x-" in the mustache templates.
+
+(All examples are in YAML format)
+
+### ObjC
+#### x-objc-operationId
+
+To customize the method name, you can provide a different name in x-objc-operationId, e.g.
+```yaml
+summary: Add a new pet to the store
+description: ''
+operationId: addPet
+x-objc-operationId: CreateNewPet
+```  
+
+### Java (Feign)
+#### x-accepts
+
+A single `Accepts` value as the Feign API client needs a single value for `Accepts` header, e.g.
+```yaml
+consumes:
+  - application/json
+  - application/xml
+x-accepts: application/json
+```
+
+#### x-content-type
+
+A single "Content-Type" value as the Feign API client needs a single value for `Content-Type` header, e.g.
+```yaml
+produces:
+  - application/xml
+  - application/json
+x-content-type: application/json
+```
+
+### Rust-server
+
+#### x-responseId
+
+Each response may specify a unique `x-responseId`. `rust-server` will use this to name the corresponding enum variant in the code. e.g.
+
+```yaml
+paths:
+  /ping:
+    get:
+      responses:
+        200:
+          description: OK
+          x-responseId: Pong
+```
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