Source

File: wp-includes/class-wp-block-list.php

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;
	}