diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/class-wp-block-list.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/class-wp-block-list.php	Tue Dec 15 13:49:49 2020 +0100
@@ -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 );
+	}
+
+}