Add initial "templates" doc.

docs/manifest.json

@@ -29,6 +29,12 @@
 		"markdown_source": "https:\/\/raw.githubusercontent.com\/WordPress\/gutenberg\/master\/docs\/block-edit-save.md",
 		"parent": "block-api"
 	},
+	{
+		"title": "Templates",
+		"slug": "templates",
+		"markdown_source": "https:\/\/raw.githubusercontent.com\/WordPress\/gutenberg\/master\/docs\/templates.md",
+		"parent": null
+	},
 	{
 		"title": "Extensibility",
 		"slug": "extensibility",

docs/templates.md

@@ -0,0 +1,71 @@
+# Templates
+
+A block template is defined as a list of block items. Such blocks can have predefined attributes, placeholder content, and be static or dynamic. Block templates allow to specify a default initial state for an editor session.
+
+The scope of templates include:
+
+- Setting a default state dynamically on the client. (like `defaultBlock`)
+- Registered as a default for a given post type.
+
+Planned additions:
+
+- Saved and assigned to pages as "page templates".
+- Defined in a `template.php` file or pulled from a custom post type (`wp_templates`) that is site specific.
+— As the equivalent of the theme hierarchy.
+
+## API
+
+Tempates can be declared in JS or in PHP as an array of blockTypes (block name and optional attributes).
+
+```js
+const template = [
+  [ 'block/name', {} ], // [ blockName, attributes ]
+];
+```
+
+```php
+'template' => array(
+	array( 'block/name' ),
+),
+```
+
+
+## Custom Post types
+
+A custom post type can register its own template during registration:
+
+```
+function register_post_type() {
+	$args = array(
+		'public' => true,
+		'label'  => 'Books',
+		'show_in_rest' => true,
+		'template' => array(
+			array( 'core/image', array(
+				'align' => 'left',
+			) ),
+			array( 'core/heading', array(
+				'placeholder' => 'Add Author...',
+			) ),
+			array( 'core/paragraph', array(
+				'placeholder' => 'Add Description...',
+			) ),
+		),
+	);
+	register_post_type( 'book', $args );
+}
+add_action( 'init', 'register_post_type' );
+```
+
+### Locking
+
+Sometimes the intention might be to lock the template on the UI so that the blocks presented cannot be manipulated. This is achieved with a `template_lock` property.
+
+```php
+'template_lock' => 'all', // or 'insert' to allow moving
+```
+
+*Options:*
+
+* `all` — prevents all operations.
+* `insert` — prevents inserting new blocks, but allows moving existing ones.