diff --git a/src/wp-includes/class-wp-block-parser.php b/src/wp-includes/class-wp-block-parser.php
index a38007ae6ad03..543f53691ccb1 100644
--- a/src/wp-includes/class-wp-block-parser.php
+++ b/src/wp-includes/class-wp-block-parser.php
@@ -343,7 +343,7 @@ public function add_freeform( $length = null ) {
 	 */
 	public function add_inner_block( WP_Block_Parser_Block $block, $token_start, $token_length, $last_offset = null ) {
 		$parent                       = $this->stack[ count( $this->stack ) - 1 ];
-		$parent->block->innerBlocks[] = (array) $this->add_html_attributes_to_block( $block );
+		$parent->block->innerBlocks[] = (array) $block;
 		$html                         = substr( $this->document, $parent->prev_offset, $token_start - $parent->prev_offset );
 
 		if ( ! empty( $html ) ) {
@@ -385,74 +385,7 @@ public function add_block_from_stack( $end_offset = null ) {
 			);
 		}
 
-		$this->output[] = (array) $this->add_html_attributes_to_block( $stack_top->block );
-	}
-
-	private function add_html_attributes_to_block( WP_Block_Parser_Block $block ): WP_Block_Parser_Block {
-		//phpcs:disable WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
-		if ( ! isset( $block->blockName ) ) {
-			return $block;
-		}
-
-		if ( '' === $block->innerHTML ) {
-			return $block;
-		}
-
-		$block_registry = WP_Block_Type_Registry::get_instance();
-		if ( null === $block_registry ) {
-			return $block;
-		}
-
-		$block_type = $block_registry->get_registered( $block->blockName );
-		if ( null === $block_type || ! isset( $block_type->attributes ) ) {
-			return $block;
-		}
-
-		foreach ( $block_type->attributes as $attribute_name => $attribute ) {
-			if ( ! isset( $attribute['selector'] ) ) {
-				continue;
-			}
-			if ( ! isset( $block->attrs[ $attribute_name ] ) ) {
-				$processor = WP_HTML_Processor::create_fragment( $block->innerHTML );
-				$selector  = $attribute['selector'];
-
-				// This is a workaround for a known unsupported selector in a core block.
-				if ( 'a:not([download])' === $selector ) {
-					$selector = 'a';
-				}
-
-				foreach ( $processor->select_all( $selector ) as $_ ) {
-					// This is a workaround for a known unsupported selector in a core block.
-					if (
-					'a:not([download])' === $attribute['selector'] &&
-					null !== $processor->get_attribute( 'download' )
-					) {
-						continue;
-					}
-
-					switch ( $attribute['source'] ) {
-						case 'attribute':
-							$attr_value = $processor->get_attribute( $attribute['attribute'] );
-							if ( null === $attr_value ) {
-								continue 2;
-							}
-							if ( null === $block->attrs ) {
-								$block->attrs = array();
-							}
-							// This could be null, string, true, check what JS parser does.
-							$block->attrs[ $attribute_name ] = $attr_value;
-							break;
-
-						// @todo see about supporting these.
-						case 'text':
-						case 'rich-text':
-						case 'query':
-							break;
-					}
-				}
-			}
-		}
-		return $block;
+		$this->output[] = (array) $stack_top->block;
 	}
 }
 
diff --git a/src/wp-includes/class-wp-block-type.php b/src/wp-includes/class-wp-block-type.php
index 6916f6a462981..6e3fde5d87b10 100644
--- a/src/wp-includes/class-wp-block-type.php
+++ b/src/wp-includes/class-wp-block-type.php
@@ -532,6 +532,76 @@ public function prepare_attributes_for_render( $attributes ) {
 		return $attributes;
 	}
 
+	/**
+	 * Adds sourced attributes from the parsed block to the block attributes.
+	 *
+	 * @since TBD
+	 *
+	 * @param array $attributes   Original block attributes.
+	 * @param array $parsed_block Parsed block.
+	 * @return array Prepared block attributes.
+	 */
+	public function add_sourced_attributes_from_parsed_block( $attributes, $parsed_block ) {
+		// If there are no attribute definitions for the block type, skip
+		// processing and return verbatim.
+		if ( ! isset( $this->attributes ) ) {
+			return $attributes;
+		}
+
+		// Sourced attributes are extracted from the block's HTML. If there's no
+		// HTML, there's nothing to do.
+		if ( '' === $parsed_block['innerHTML'] ) {
+			return $attributes;
+		}
+
+		foreach ( $this->attributes as $attribute_name => $attribute_definition ) {
+			if (
+				! isset( $attribute_definition['source'] ) ||
+				'attribute' !== $attribute_definition['source'] ||
+				! is_string( $attribute_definition['attribute'] ) ||
+				! isset( $attribute_definition['selector'] ) ||
+
+				// @todo what to do if it's in serialized attributes already? Skip for now.
+				isset( $attributes[ $attribute_name ] )
+			) {
+				continue;
+			}
+
+			$processor = WP_HTML_Processor::create_fragment( $parsed_block['innerHTML'] );
+			if ( null === $processor ) {
+				continue;
+			}
+
+			$selector = $attribute_definition['selector'];
+
+			// This is a workaround for a known unsupported selector in a core block.
+			if ( 'a:not([download])' === $selector ) {
+				$selector = 'a';
+			}
+
+			foreach ( $processor->select_all( $selector ) as $_ ) {
+				// This is a workaround for a known unsupported selector in a core block.
+				if (
+					'a:not([download])' === $attribute_definition['selector'] &&
+					null !== $processor->get_attribute( 'download' )
+				) {
+					continue;
+				}
+
+				$value = $processor->get_attribute( $attribute_definition['attribute'] );
+				if ( null === $value ) {
+					continue 2;
+				}
+
+				// @todo another function validates value types, is that sufficient?
+				$attributes[ $attribute_name ] = $value;
+
+			}
+		}
+
+		return $attributes;
+	}
+
 	/**
 	 * Sets block type properties.
 	 *
diff --git a/src/wp-includes/class-wp-block.php b/src/wp-includes/class-wp-block.php
index a1c52019c29a5..01edb92cff23d 100644
--- a/src/wp-includes/class-wp-block.php
+++ b/src/wp-includes/class-wp-block.php
@@ -191,7 +191,8 @@ public function __get( $name ) {
 				array();
 
 			if ( ! is_null( $this->block_type ) ) {
-				$this->attributes = $this->block_type->prepare_attributes_for_render( $this->attributes );
+				$this->attributes = $this->block_type->add_sourced_attributes_from_parsed_block( $this->attributes, $this->parsed_block );
+				$this->attributes = $this->block_type->prepare_attributes_for_render( $this->attributes, $this->parsed_block );
 			}
 
 			return $this->attributes;