diff --git a/src/wp-includes/class-wp-block-list.php b/src/wp-includes/class-wp-block-list.php
new file mode 100644
index 0000000000000..378faba578b11
--- /dev/null
+++ b/src/wp-includes/class-wp-block-list.php
@@ -0,0 +1,203 @@
+<?php
+/**
+ * Blocks API: WP_Block_List class
+ *
+ * @package WordPress
+ * @since 5.5.0
+ */
+
+/**
+ * Class representing a list of block instances.
+ *
+ * @since 5.5.0
+ */
+class WP_Block_List implements Iterator, ArrayAccess, Countable {
+
+	/**
+	 * Original array of parsed block data, or block instances.
+	 *
+	 * @since 5.5.0
+	 * @var array[]|WP_Block[]
+	 * @access protected
+	 */
+	protected $blocks;
+
+	/**
+	 * All available context of the current hierarchy.
+	 *
+	 * @since 5.5.0
+	 * @var array
+	 * @access protected
+	 */
+	protected $available_context;
+
+	/**
+	 * Block type registry to use in constructing block instances.
+	 *
+	 * @since 5.5.0
+	 * @var WP_Block_Type_Registry
+	 * @access protected
+	 */
+	protected $registry;
+
+	/**
+	 * Constructor.
+	 *
+	 * Populates object properties from the provided block instance argument.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @param array[]|WP_Block[]     $blocks            Array of parsed block data, or block instances.
+	 * @param array                  $available_context Optional array of ancestry context values.
+	 * @param WP_Block_Type_Registry $registry          Optional block type registry.
+	 */
+	public function __construct( $blocks, $available_context = array(), $registry = null ) {
+		if ( ! $registry instanceof WP_Block_Type_Registry ) {
+			$registry = WP_Block_Type_Registry::get_instance();
+		}
+
+		$this->blocks            = $blocks;
+		$this->available_context = $available_context;
+		$this->registry          = $registry;
+	}
+
+	/**
+	 * Returns true if a block exists by the specified block index, or false
+	 * otherwise.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/arrayaccess.offsetexists.php
+	 *
+	 * @param string $index Index of block to check.
+	 * @return bool Whether block exists.
+	 */
+	public function offsetExists( $index ) {
+		return isset( $this->blocks[ $index ] );
+	}
+
+	/**
+	 * Returns the value by the specified block index.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/arrayaccess.offsetget.php
+	 *
+	 * @param string $index Index of block value to retrieve.
+	 * @return mixed|null Block value if exists, or null.
+	 */
+	public function offsetGet( $index ) {
+		$block = $this->blocks[ $index ];
+
+		if ( isset( $block ) && is_array( $block ) ) {
+			$block                  = new WP_Block( $block, $this->available_context, $this->registry );
+			$this->blocks[ $index ] = $block;
+		}
+
+		return $block;
+	}
+
+	/**
+	 * Assign a block value by the specified block index.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/arrayaccess.offsetset.php
+	 *
+	 * @param string $index Index of block value to set.
+	 * @param mixed  $value Block value.
+	 */
+	public function offsetSet( $index, $value ) {
+		if ( is_null( $index ) ) {
+			$this->blocks[] = $value;
+		} else {
+			$this->blocks[ $index ] = $value;
+		}
+	}
+
+	/**
+	 * Unset a block.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/arrayaccess.offsetunset.php
+	 *
+	 * @param string $index Index of block value to unset.
+	 */
+	public function offsetUnset( $index ) {
+		unset( $this->blocks[ $index ] );
+	}
+
+	/**
+	 * Rewinds back to the first element of the Iterator.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/iterator.rewind.php
+	 */
+	public function rewind() {
+		reset( $this->blocks );
+	}
+
+	/**
+	 * Returns the current element of the block list.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/iterator.current.php
+	 *
+	 * @return mixed Current element.
+	 */
+	public function current() {
+		return $this->offsetGet( $this->key() );
+	}
+
+	/**
+	 * Returns the key of the current element of the block list.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/iterator.key.php
+	 *
+	 * @return mixed Key of the current element.
+	 */
+	public function key() {
+		return key( $this->blocks );
+	}
+
+	/**
+	 * Moves the current position of the block list to the next element.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/iterator.next.php
+	 */
+	public function next() {
+		next( $this->blocks );
+	}
+
+	/**
+	 * Checks if current position is valid.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/iterator.valid.php
+	 */
+	public function valid() {
+		return null !== key( $this->blocks );
+	}
+
+	/**
+	 * Returns the count of blocks in the list.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @link https://www.php.net/manual/en/countable.count.php
+	 *
+	 * @return int Block count.
+	 */
+	public function count() {
+		return count( $this->blocks );
+	}
+
+}
diff --git a/src/wp-includes/class-wp-block.php b/src/wp-includes/class-wp-block.php
new file mode 100644
index 0000000000000..979fca90708f1
--- /dev/null
+++ b/src/wp-includes/class-wp-block.php
@@ -0,0 +1,233 @@
+<?php
+/**
+ * Blocks API: WP_Block class
+ *
+ * @package WordPress
+ * @since 5.5.0
+ */
+
+/**
+ * Class representing a parsed instance of a block.
+ *
+ * @since 5.5.0
+ * @property array $attributes
+ */
+class WP_Block {
+
+	/**
+	 * Original parsed array representation of block.
+	 *
+	 * @since 5.5.0
+	 * @var array
+	 */
+	public $parsed_block;
+
+	/**
+	 * Name of block.
+	 *
+	 * @example "core/paragraph"
+	 *
+	 * @since 5.5.0
+	 * @var string
+	 */
+	public $name;
+
+	/**
+	 * Block type associated with the instance.
+	 *
+	 * @since 5.5.0
+	 * @var WP_Block_Type
+	 */
+	public $block_type;
+
+	/**
+	 * Block context values.
+	 *
+	 * @since 5.5.0
+	 * @var array
+	 */
+	public $context = array();
+
+	/**
+	 * All available context of the current hierarchy.
+	 *
+	 * @since 5.5.0
+	 * @var array
+	 * @access protected
+	 */
+	protected $available_context;
+
+	/**
+	 * List of inner blocks (of this same class)
+	 *
+	 * @since 5.5.0
+	 * @var WP_Block[]
+	 */
+	public $inner_blocks = array();
+
+	/**
+	 * Resultant HTML from inside block comment delimiters after removing inner
+	 * blocks.
+	 *
+	 * @example "...Just <!-- wp:test /--> testing..." -> "Just testing..."
+	 *
+	 * @since 5.5.0
+	 * @var string
+	 */
+	public $inner_html = '';
+
+	/**
+	 * List of string fragments and null markers where inner blocks were found
+	 *
+	 * @example array(
+	 *   'inner_html'    => 'BeforeInnerAfter',
+	 *   'inner_blocks'  => array( block, block ),
+	 *   'inner_content' => array( 'Before', null, 'Inner', null, 'After' ),
+	 * )
+	 *
+	 * @since 5.5.0
+	 * @var array
+	 */
+	public $inner_content = array();
+
+	/**
+	 * Constructor.
+	 *
+	 * Populates object properties from the provided block instance argument.
+	 *
+	 * The given array of context values will not necessarily be available on
+	 * the instance itself, but is treated as the full set of values provided by
+	 * the block's ancestry. This is assigned to the private `available_context`
+	 * property. Only values which are configured to consumed by the block via
+	 * its registered type will be assigned to the block's `context` property.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @param array                  $block             Array of parsed block properties.
+	 * @param array                  $available_context Optional array of ancestry context values.
+	 * @param WP_Block_Type_Registry $registry          Optional block type registry.
+	 */
+	public function __construct( $block, $available_context = array(), $registry = null ) {
+		$this->parsed_block = $block;
+		$this->name         = $block['blockName'];
+
+		if ( is_null( $registry ) ) {
+			$registry = WP_Block_Type_Registry::get_instance();
+		}
+
+		$this->block_type = $registry->get_registered( $this->name );
+
+		$this->available_context = $available_context;
+
+		if ( ! empty( $this->block_type->uses_context ) ) {
+			foreach ( $this->block_type->uses_context as $context_name ) {
+				if ( array_key_exists( $context_name, $this->available_context ) ) {
+					$this->context[ $context_name ] = $this->available_context[ $context_name ];
+				}
+			}
+		}
+
+		if ( ! empty( $block['innerBlocks'] ) ) {
+			$child_context = $this->available_context;
+
+			if ( ! empty( $this->block_type->provides_context ) ) {
+				foreach ( $this->block_type->provides_context as $context_name => $attribute_name ) {
+					if ( array_key_exists( $attribute_name, $this->attributes ) ) {
+						$child_context[ $context_name ] = $this->attributes[ $attribute_name ];
+					}
+				}
+			}
+
+			$this->inner_blocks = new WP_Block_List( $block['innerBlocks'], $child_context, $registry );
+		}
+
+		if ( ! empty( $block['innerHTML'] ) ) {
+			$this->inner_html = $block['innerHTML'];
+		}
+
+		if ( ! empty( $block['innerContent'] ) ) {
+			$this->inner_content = $block['innerContent'];
+		}
+	}
+
+	/**
+	 * Returns a value from an inaccessible property.
+	 *
+	 * This is used to lazily initialize the `attributes` property of a block,
+	 * such that it is only prepared with default attributes at the time that
+	 * the property is accessed. For all other inaccessible properties, a `null`
+	 * value is returned.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @param string $name Property name.
+	 * @return array|null Prepared attributes, or null.
+	 */
+	public function __get( $name ) {
+		if ( 'attributes' === $name ) {
+			$this->attributes = isset( $this->parsed_block['attrs'] ) ?
+				$this->parsed_block['attrs'] :
+				array();
+
+			if ( ! is_null( $this->block_type ) ) {
+				$this->attributes = $this->block_type->prepare_attributes_for_render( $this->attributes );
+			}
+
+			return $this->attributes;
+		}
+
+		return null;
+	}
+
+	/**
+	 * Generates the render output for the block.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @param array $options {
+	 *   Optional options object.
+	 *
+	 *   @type bool $dynamic Defaults to 'true'. Optionally set to false to avoid using the block's render_callback.
+	 * }
+	 * @return string Rendered block output.
+	 */
+	public function render( $options = array() ) {
+		global $post;
+		$options = wp_parse_args(
+			$options,
+			array(
+				'dynamic' => true,
+			)
+		);
+
+		$is_dynamic    = $options['dynamic'] && $this->name && null !== $this->block_type && $this->block_type->is_dynamic();
+		$block_content = '';
+
+		if ( ! $options['dynamic'] || empty( $this->block_type->skip_inner_blocks ) ) {
+			$index = 0;
+			foreach ( $this->inner_content as $chunk ) {
+				$block_content .= is_string( $chunk ) ?
+					$chunk :
+					$this->inner_blocks[ $index++ ]->render();
+			}
+		}
+
+		if ( $is_dynamic ) {
+			$global_post   = $post;
+			$block_content = (string) call_user_func( $this->block_type->render_callback, $this->attributes, $block_content, $this );
+			$post          = $global_post;
+		}
+
+		if ( ! empty( $this->block_type->script ) ) {
+			wp_enqueue_script( $this->block_type->script );
+		}
+
+		if ( ! empty( $this->block_type->style ) ) {
+			wp_enqueue_style( $this->block_type->style );
+		}
+
+		/** This filter is documented in src/wp-includes/blocks.php */
+		return apply_filters( 'render_block', $block_content, $this->parsed_block );
+	}
+
+}
diff --git a/src/wp-settings.php b/src/wp-settings.php
index a78be1c0918c0..a1cec18559a21 100644
--- a/src/wp-settings.php
+++ b/src/wp-settings.php
@@ -276,6 +276,8 @@
 require ABSPATH . WPINC . '/class-wp-block-type.php';
 require ABSPATH . WPINC . '/class-wp-block-styles-registry.php';
 require ABSPATH . WPINC . '/class-wp-block-type-registry.php';
+require ABSPATH . WPINC . '/class-wp-block.php';
+require ABSPATH . WPINC . '/class-wp-block-list.php';
 require ABSPATH . WPINC . '/class-wp-block-parser.php';
 require ABSPATH . WPINC . '/blocks.php';
 require ABSPATH . WPINC . '/blocks/archives.php';
diff --git a/tests/phpunit/tests/blocks/block-list.php b/tests/phpunit/tests/blocks/block-list.php
new file mode 100644
index 0000000000000..c5d5e543acdea
--- /dev/null
+++ b/tests/phpunit/tests/blocks/block-list.php
@@ -0,0 +1,112 @@
+<?php
+/**
+ * WP_Block_List tests.
+ *
+ * @package WordPress
+ * @subpackage Blocks
+ * @since 5.5.0
+ */
+
+/**
+ * Tests for WP_Block_List
+ *
+ * @since 5.5.0
+ *
+ * @group blocks
+ */
+class WP_Block_List_Test extends WP_UnitTestCase {
+
+	/**
+	 * Fake block type registry.
+	 *
+	 * @var WP_Block_Type_Registry
+	 */
+	private $registry = null;
+
+	/**
+	 * Set up each test method.
+	 */
+	public function setUp() {
+		parent::setUp();
+
+		$this->registry = new WP_Block_Type_Registry();
+		$this->registry->register( 'core/example', array() );
+	}
+
+	/**
+	 * Tear down each test method.
+	 */
+	public function tearDown() {
+		parent::tearDown();
+
+		$this->registry = null;
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_array_access() {
+		$parsed_blocks = parse_blocks( '<!-- wp:example /-->' );
+		$context       = array();
+		$blocks        = new WP_Block_List( $parsed_blocks, $context, $this->registry );
+
+		// Test "offsetExists".
+		$this->assertTrue( isset( $blocks[0] ) );
+
+		// Test "offsetGet".
+		$this->assertEquals( 'core/example', $blocks[0]->name );
+
+		// Test "offsetSet".
+		$parsed_blocks[0]['blockName'] = 'core/updated';
+		$blocks[0]                     = new WP_Block( $parsed_blocks[0], $context, $this->registry );
+		$this->assertEquals( 'core/updated', $blocks[0]->name );
+
+		// Test "offsetUnset".
+		unset( $blocks[0] );
+		$this->assertFalse( isset( $blocks[0] ) );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_iterable() {
+		$parsed_blocks = parse_blocks( '<!-- wp:example --><!-- wp:example /--><!-- /wp:example -->' );
+		$context       = array();
+		$blocks        = new WP_Block_List( $parsed_blocks, $context, $this->registry );
+		$assertions    = 0;
+
+		foreach ( $blocks as $block ) {
+			$this->assertEquals( 'core/example', $block->name );
+			$assertions++;
+			foreach ( $block->inner_blocks as $inner_block ) {
+				$this->assertEquals( 'core/example', $inner_block->name );
+				$assertions++;
+			}
+		}
+
+		$blocks->rewind();
+		while ( $blocks->valid() ) {
+			$key   = $blocks->key();
+			$block = $blocks->current();
+			$this->assertEquals( 0, $key );
+			$assertions++;
+			$this->assertEquals( 'core/example', $block->name );
+			$assertions++;
+			$blocks->next();
+		}
+
+		$this->assertEquals( 4, $assertions );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_countable() {
+		$parsed_blocks = parse_blocks( '<!-- wp:example /-->' );
+		$context       = array();
+		$blocks        = new WP_Block_List( $parsed_blocks, $context, $this->registry );
+
+		$this->assertEquals( 1, count( $blocks ) );
+	}
+
+}
diff --git a/tests/phpunit/tests/blocks/block.php b/tests/phpunit/tests/blocks/block.php
new file mode 100644
index 0000000000000..2a702a5bc43c3
--- /dev/null
+++ b/tests/phpunit/tests/blocks/block.php
@@ -0,0 +1,397 @@
+<?php
+/**
+ * WP_Block Tests
+ *
+ * @package WordPress
+ * @subpackage Blocks
+ * @since 5.5.0
+ */
+
+/**
+ * Tests for WP_Block
+ *
+ * @since 5.5.0
+ *
+ * @group blocks
+ */
+class WP_Block_Test extends WP_UnitTestCase {
+
+	/**
+	 * Fake block type registry.
+	 *
+	 * @var WP_Block_Type_Registry
+	 */
+	private $registry = null;
+
+	/**
+	 * Set up each test method.
+	 */
+	public function setUp() {
+		parent::setUp();
+
+		$this->registry = new WP_Block_Type_Registry();
+	}
+
+	/**
+	 * Tear down each test method.
+	 */
+	public function tearDown() {
+		parent::tearDown();
+
+		$this->registry = null;
+	}
+
+	function filter_render_block( $content, $parsed_block ) {
+		return 'Original: "' . $content . '", from block "' . $parsed_block['blockName'] . '"';
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_constructor_assigns_properties_from_parsed_block() {
+		$this->registry->register( 'core/example', array() );
+
+		$parsed_blocks = parse_blocks( '<!-- wp:example {"ok":true} -->a<!-- wp:example /-->b<!-- /wp:example -->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertSame( $parsed_block, $block->parsed_block );
+		$this->assertEquals( $parsed_block['blockName'], $block->name );
+		$this->assertEquals( $parsed_block['attrs'], $block->attributes );
+		$this->assertEquals( $parsed_block['innerContent'], $block->inner_content );
+		$this->assertEquals( $parsed_block['innerHTML'], $block->inner_html );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_constructor_assigns_block_type_from_registry() {
+		$block_type_settings = array(
+			'attributes' => array(
+				'defaulted' => array(
+					'type'    => 'number',
+					'default' => 10,
+				),
+			),
+		);
+		$this->registry->register( 'core/example', $block_type_settings );
+
+		$parsed_block = array( 'blockName' => 'core/example' );
+		$context      = array();
+		$block        = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertInstanceOf( WP_Block_Type::class, $block->block_type );
+		$this->assertEquals(
+			$block_type_settings['attributes'],
+			$block->block_type->attributes
+		);
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_lazily_assigns_attributes_with_defaults() {
+		$this->registry->register(
+			'core/example',
+			array(
+				'attributes' => array(
+					'defaulted' => array(
+						'type'    => 'number',
+						'default' => 10,
+					),
+				),
+			)
+		);
+
+		$parsed_block = array(
+			'blockName' => 'core/example',
+			'attrs'     => array(
+				'explicit' => 20,
+			),
+		);
+		$context      = array();
+		$block        = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertEquals(
+			array(
+				'defaulted' => 10,
+				'explicit'  => 20,
+			),
+			$block->attributes
+		);
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_lazily_assigns_attributes_with_only_defaults() {
+		$this->registry->register(
+			'core/example',
+			array(
+				'attributes' => array(
+					'defaulted' => array(
+						'type'    => 'number',
+						'default' => 10,
+					),
+				),
+			)
+		);
+
+		$parsed_block = array(
+			'blockName' => 'core/example',
+			'attrs'     => array(),
+		);
+		$context      = array();
+		$block        = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertEquals( array( 'defaulted' => 10 ), $block->attributes );
+		// Intentionally call a second time, to ensure property was assigned.
+		$this->assertEquals( array( 'defaulted' => 10 ), $block->attributes );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_constructor_assigns_context_from_block_type() {
+		$this->registry->register(
+			'core/example',
+			array(
+				'uses_context' => array( 'requested' ),
+			)
+		);
+
+		$parsed_block = array( 'blockName' => 'core/example' );
+		$context      = array(
+			'requested'   => 'included',
+			'unrequested' => 'not included',
+		);
+		$block        = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertEquals( array( 'requested' => 'included' ), $block->context );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_constructor_maps_inner_blocks() {
+		$this->registry->register( 'core/example', array() );
+
+		$parsed_blocks = parse_blocks( '<!-- wp:example {"ok":true} -->a<!-- wp:example /-->b<!-- /wp:example -->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertCount( 1, $block->inner_blocks );
+		$this->assertInstanceOf( WP_Block::class, $block->inner_blocks[0] );
+		$this->assertEquals( 'core/example', $block->inner_blocks[0]->name );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_constructor_prepares_context_for_inner_blocks() {
+		$this->registry->register(
+			'core/outer',
+			array(
+				'attributes'       => array(
+					'recordId' => array(
+						'type' => 'number',
+					),
+				),
+				'provides_context' => array(
+					'core/recordId' => 'recordId',
+				),
+			)
+		);
+		$this->registry->register(
+			'core/inner',
+			array(
+				'uses_context' => array( 'core/recordId' ),
+			)
+		);
+
+		$parsed_blocks = parse_blocks( '<!-- wp:outer {"recordId":10} --><!-- wp:inner /--><!-- /wp:outer -->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array( 'unrequested' => 'not included' );
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertCount( 0, $block->context );
+		$this->assertEquals(
+			array( 'core/recordId' => 10 ),
+			$block->inner_blocks[0]->context
+		);
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_constructor_assigns_merged_context() {
+		$this->registry->register(
+			'core/example',
+			array(
+				'attributes'       => array(
+					'value' => array(
+						'type' => array( 'string', 'null' ),
+					),
+				),
+				'provides_context' => array(
+					'core/value' => 'value',
+				),
+				'uses_context'     => array( 'core/value' ),
+			)
+		);
+
+		$parsed_blocks = parse_blocks(
+			'<!-- wp:example {"value":"merged"} -->' .
+			'<!-- wp:example {"value":null} -->' .
+			'<!-- wp:example /-->' .
+			'<!-- /wp:example -->' .
+			'<!-- /wp:example -->'
+		);
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array( 'core/value' => 'original' );
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertEquals(
+			array( 'core/value' => 'original' ),
+			$block->context
+		);
+		$this->assertEquals(
+			array( 'core/value' => 'merged' ),
+			$block->inner_blocks[0]->context
+		);
+		$this->assertEquals(
+			array( 'core/value' => null ),
+			$block->inner_blocks[0]->inner_blocks[0]->context
+		);
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_render_static_block_type_returns_own_content() {
+		$this->registry->register( 'core/static', array() );
+		$this->registry->register(
+			'core/dynamic',
+			array(
+				'render_callback' => function() {
+					return 'b';
+				},
+			)
+		);
+
+		$parsed_blocks = parse_blocks( '<!-- wp:static -->a<!-- wp:dynamic /-->c<!-- /wp:static -->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertSame( 'abc', $block->render() );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_render_passes_block_for_render_callback() {
+		$this->registry->register(
+			'core/greeting',
+			array(
+				'render_callback' => function( $attributes, $content, $block ) {
+					return sprintf( 'Hello from %s', $block->name );
+				},
+			)
+		);
+
+		$parsed_blocks = parse_blocks( '<!-- wp:greeting /-->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertSame( 'Hello from core/greeting', $block->render() );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_render_applies_render_block_filter() {
+		$this->registry->register( 'core/example', array() );
+
+		add_filter( 'render_block', array( $this, 'filter_render_block' ), 10, 2 );
+
+		$parsed_blocks = parse_blocks( '<!-- wp:example -->Static<!-- wp:example -->Inner<!-- /wp:example --><!-- /wp:example -->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$rendered_content = $block->render();
+
+		remove_filter( 'render_block', array( $this, 'filter_render_block' ) );
+
+		$this->assertSame( 'Original: "StaticOriginal: "Inner", from block "core/example"", from block "core/example"', $rendered_content );
+
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_passes_attributes_to_render_callback() {
+		$this->registry->register(
+			'core/greeting',
+			array(
+				'attributes'      => array(
+					'toWhom'      => array(
+						'type' => 'string',
+					),
+					'punctuation' => array(
+						'type'    => 'string',
+						'default' => '!',
+					),
+				),
+				'render_callback' => function( $block_attributes ) {
+					return sprintf(
+						'Hello %s%s',
+						$block_attributes['toWhom'],
+						$block_attributes['punctuation']
+					);
+				},
+			)
+		);
+
+		$parsed_blocks = parse_blocks( '<!-- wp:greeting {"toWhom":"world"} /-->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertSame( 'Hello world!', $block->render() );
+	}
+
+	/**
+	 * @ticket 49927
+	 */
+	function test_passes_content_to_render_callback() {
+		$this->registry->register(
+			'core/outer',
+			array(
+				'render_callback' => function( $block_attributes, $content ) {
+					return $content;
+				},
+			)
+		);
+		$this->registry->register(
+			'core/inner',
+			array(
+				'render_callback' => function() {
+					return 'b';
+				},
+			)
+		);
+
+		$parsed_blocks = parse_blocks( '<!-- wp:outer -->a<!-- wp:inner /-->c<!-- /wp:outer -->' );
+		$parsed_block  = $parsed_blocks[0];
+		$context       = array();
+		$block         = new WP_Block( $parsed_block, $context, $this->registry );
+
+		$this->assertSame( 'abc', $block->render() );
+	}
+
+}