website/docs: document providers schema output format (hashicorp#22361)

* website/docs: document providers schema output format

* Update website/docs/commands/providers/schema.html.md

Co-Authored-By: Nick Fagerlund <nick@hashicorp.com>

website/docs/commands/providers/schema.html.md

@@ -22,3 +22,119 @@ The list of available flags are:
 * `-json` - Displays the schemas in a machine-readble, JSON format.
 
 Please note that, at this time, the `-json` flag is a _required_ option. In future releases, this command will be extended to allow for additional options. 
+
+-> **Note:** The output includes a `format_version` key, which currently has major version zero to indicate that the format is experimental and subject to change. A future version will assign a non-zero major version and make stronger promises about compatibility. We do not anticipate any significant breaking changes to the format before its first major version, however.
+
+## Format Summary
+
+The following sections describe the JSON output format by example, using a pseudo-JSON notation.
+Important elements are described with comments, which are prefixed with //.
+To avoid excessive repetition, we've split the complete format into several discrete sub-objects, described under separate headers. References wrapped in angle brackets (like `<block-representation>`) are placeholders which, in the real output, would be replaced by an instance of the specified sub-object.
+
+The JSON output format consists of the following objects and sub-objects:
+
+- [Providers Schema Representation](#providers-schema-representation) - the top-level object returned by `terraform providers schema -json`
+- [Schema Representation](#schema-representation) - a sub-object of providers, resources, and data sources that describes their schema
+- [Block Representation](#block-representation) - a sub-object of schemas that describes attributes and nested blocks
+
+## Providers Schema Representation 
+
+```javascript
+{
+  "format_version": "0.1",
+
+  // "provider_schemas" describes the provider schemas for all 
+  // providers throughout the configuration tree. 
+  "provider_schemas": {
+    // keys in this map are the provider type, such as "random"
+    "example_provider_name": {
+      // "provider" is the schema for the provider configuration
+      "provider": <schema-representation>,
+
+      // "resource_schemas" map the resource type name to the resource's schema
+      "resource_schemas": {
+        "example_resource_name": <schema-representation>
+      },
+
+      // "data_source_schemas" map the data source type name to the
+      // data source's schema
+      "data_source_schemas": {
+        "example_datasource_name": <schema-representation>,
+      }
+    },
+    "example_provider_two": { … }
+  }
+}
+```
+
+## Schema Representation
+
+A schema representation pairs a provider or resource schema (in a "block") with that schema's version.
+
+```javascript
+{
+  // "version" is the schema version, not the provider version
+  "version": int64,
+  "block": <block-representation>
+}
+```
+
+## Block Representation
+
+A block representation contains "attributes" and "block_types" (which represent nested blocks).
+
+```javascript
+{
+  // "attributes" describes any attributes that appear directly inside the 
+  // block. Keys in this map are the attribute names.
+  "attributes":  {
+    "example_attribute_name": {
+      // "type" is a representation of a type specification
+      // that the attribute's value must conform to.
+      "type": "string",
+
+      // "description" is an English-language description of 
+      // the purpose and usage of the attribute.
+      "description": "string",
+
+      // "required", if set to true, specifies that an 
+      // omitted or null value is not permitted.
+      "required": bool,
+
+      // "optional", if set to true, specifies that an 
+      // omitted or null value is permitted.  
+      "optional": bool,
+
+      // "computed", if set to true, indicates that the 
+      // value comes from the provider rather than the 
+      // configuration.
+      "computed": bool,
+
+      // "sensitive", if set to true, indicates that the
+      // attribute may contain sensitive information.
+      "sensitive": bool
+    },
+  },
+  // "block_types" describes any nested blocks that appear directly
+  // inside the block.
+  // Keys in this map are the names of the block_type.
+  "block_types": { 
+    "example_block_name": {	
+      // "nesting_mode" describes the nesting mode for the 
+      // child block, and can be one of the following:
+      // 	single
+      // 	list
+      // 	set
+      // 	map
+    "nesting_mode": "list",
+    "block": <block-representation>,
+
+    // "min_items" and "max_items" set lower and upper 
+    // limits on the number of child blocks allowed for 
+    // the list and set modes. These are 
+    // omitted for other modes. 
+    "min_items": 1,
+    "max_items": 3
+  }
+}
+```