message: add docs for x-ms-client-default
diff: @@ -19,6 +19,7 @@ The following documents describes AutoRest specific vendor extensions for [OpenA
  * [x-ms-examples](#x-ms-examples) - describes the format for specifying examples for request and response of an operation in an OpenAPI definition.
  * [x-ms-error-response](#x-ms-error-response) - indicates whether the response status code should be treated as an error response
  * [x-ms-text](#x-ms-text) - XML helper for scenario with attributes and text on the same XML node
  +* [x-ms-client-default](#x-ms-client-default) - Set default value for properties and parameters
  ### Microsoft Azure Extensions (available in most generators only when using `--azure-arm`)
  * [x-ms-odata](#x-ms-odata) - indicates the operation includes one or more [OData](http://www.odata.org/) query parameters.
  @@ -791,6 +792,59 @@ Note: The extension is not tight to this particular scenario (you could model an
  . . .
  ```
  +## x-ms-client-default
  +Set the default value for a property or a parameter.
  +
  +With this extension, you can set a default value for a property or parameter that is independent of how the property / parameter's schema is handling a default
  +
  +**Parent element**: [Parameter Objects](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#parameterObject) or [Property on the Schema Definition](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#schemaObject).
  +
  +**Schema**:
  +`string` - the default value for the property / parameter
  +
  +**Parameter Example**:
  +```json5
  +. . .
  + "parameters": [
  + {
  + "name": "parameterWithClientDefault",
  + "in": "query",
  + "type": "string",
  + "enum": [
  + "value1",
  + "value2"
  + ],
  + "x-ms-enum": {
  + "name": "ParameterWithClientDefaultEnum",
  + "modelAsString": false
  + },
  + "required": true,
  + "x-ms-client-default": "value1"
  + }
  + ],
  +. . .
  +```
  +
  +**Property Example**:
  +```json5
  +. . .
  + "properties": {
  + "propertyWithClientDefault": {
  + "type": "string",
  + "enum": [
  + "value1",
  + "value2"
  + ],
  + "x-ms-enum": {
  + "name": "PropertyWithClientDefaultEnum",
  + "modelAsString": true
  + },
  + "x-ms-client-default": "value1"
  + }
  + }
  +. . .
  +```
  +
  ## x-ms-pageable
  The REST API guidelines define a common pattern for paging through lists of data. The operation response is modeled in OpenAPI as a list of items (a "page") and a link to the next page, effectively resembling a singly linked list. Tag the operation as `x-ms-pageable` and the generated code will include methods for navigating between pages.
  