[json] update server readme

extensions/json-language-features/server/README.md

@@ -21,6 +21,8 @@ The server implements the following capabilities of the language server protocol
 - [Document Symbols](https://microsoft.github.io/language-server-protocol/specification#textDocument_documentSymbol) for quick navigation to properties in the document.
 - [Document Colors](https://microsoft.github.io/language-server-protocol/specification#textDocument_documentColor) for showing color decorators on values representing colors and [Color Presentation](https://microsoft.github.io/language-server-protocol/specification#textDocument_colorPresentation) for color presentation information to support color pickers. The location of colors is defined by the document's [JSON schema](http://json-schema.org/). All values marked with `"format": "color-hex"` (VSCode specific, non-standard JSON Schema extension) are considered color values. The supported color formats are `#rgb[a]` and `#rrggbb[aa]`.
 - [Code Formatting](https://microsoft.github.io/language-server-protocol/specification#textDocument_rangeFormatting) supporting ranges and formatting the whole document.
+- [Folding Ranges](https://microsoft.github.io/language-server-protocol/specification#textDocument_foldingRange) for all folding ranges in the document.
+- Semantic Selection for semantic selection for one or multiple cursor positions.
 - [Diagnostics (Validation)](https://microsoft.github.io/language-server-protocol/specification#textDocument_publishDiagnostics) are pushed for all open documents
    - syntax errors
    - structural validation based on the document's [JSON schema](http://json-schema.org/).
@@ -90,34 +92,33 @@ To find the schema for a given JSON document, the server uses the following mech
 - The settings define a schema association based on the documents URL. Settings can either associate a schema URL to a file or path pattern, and they can directly provide a schema.
 - Additionally, schema associations can also be provided by a custom 'schemaAssociations' configuration call.
 
-Schemas are identified by URLs. To load the content of a schema, the JSON language server tries to load from that URL or path. The following URL schemas are supported:
-- `http`, `https`: Loaded using NodeJS's HTTP support. Proxies can be configured through the settings.
-- `file`: Loaded using NodeJS's `fs` support.
-- `vscode`: Loaded by an LSP call to the client.
-
-#### Schema associations notification
+Schemas are identified by URLs. To load the content of a schema, the JSON language server either tries to load from that URI or path itself, or delegates to the client.
 
-In addition to the settings, schemas associations can also be provided through a notification from the client to the server. This notification is a JSON language server specific, non-standardized, extension to the LSP.
+The `initializationOptions.handledSchemaProtocols` initialization option defines which URLs are handled by the server. Requests for all other URIs are send to the client.
 
-Notification:
-- method: 'json/schemaAssociations'
-- params: `ISchemaAssociations` defined as follows
+`handledSchemaProtocols` is part of the initialization options and can't be changed while the server is running.
 
 ```ts
-interface ISchemaAssociations {
-	[pattern: string]: string[];
+let clientOptions: LanguageClientOptions = {
+		initializationOptions: {
+			handledSchemaProtocols: ['file'] // language server should only try to load file URLs
+		}
+        ...
 }
 ```
-  - keys: a file names or file path (separated by `/`). `*` can be used as a wildcard.
-  - values: An array of schema URLs
+
+If `handledSchemaProtocols` is not set, the JSON language server will load the following URLs itself:
+
+- `http`, `https`: Loaded using NodeJS's HTTP support. Proxies can be configured through the settings.
+- `file`: Loaded using NodeJS's `fs` support.
 
 #### Schema content request
 
-The schema content for schema URLs that start with `vscode://` will be requested from the client through an LSP request. This request is a JSON language server specific, non-standardized, extension to the LSP.
+Requests for schemas with URLs not handled by the server are forwarded to the client through an LSP request. This request is a JSON language server specific, non-standardized, extension to the LSP.
 
 Request:
 - method: 'vscode/content'
-- params: `string` - The schema URL to request. The server will only ask for URLs that start with `vscode://`
+- params: `string` - The schema URL to request.
 - response: `string` - The content of the schema with the given URL
 
 #### Schema content change notification
@@ -125,6 +126,22 @@ Request:
 When the client is aware that a schema content has changed, it will notify the server through a notification. This notification is a JSON language server specific, non-standardized, extension to the LSP.
 The server will, as a response, clear the schema content from the cache and reload the schema content when required again.
 
+#### Schema associations notification
+
+In addition to the settings, schemas associations can also be provided through a notification from the client to the server. This notification is a JSON language server specific, non-standardized, extension to the LSP.
+
+Notification:
+- method: 'json/schemaAssociations'
+- params: `ISchemaAssociations` defined as follows
+
+```ts
+interface ISchemaAssociations {
+	[pattern: string]: string[];
+}
+```
+  - keys: a file names or file path (separated by `/`). `*` can be used as a wildcard.
+  - values: An array of schema URLs
+
 Notification:
 - method: 'json/schemaContent'
 - params: `string` the URL of the schema that has changed.