diff --git a/wp-includes/class-wp-block.php b/wp-includes/class-wp-block.php
index cd0128f1f8..be73c13070 100644
--- a/wp-includes/class-wp-block.php
+++ b/wp-includes/class-wp-block.php
@@ -333,68 +333,27 @@ class WP_Block {
 		switch ( $block_type->attributes[ $attribute_name ]['source'] ) {
 			case 'html':
 			case 'rich-text':
-				$block_reader = new WP_HTML_Tag_Processor( $block_content );
-
-				// TODO: Support for CSS selectors whenever they are ready in the HTML API.
-				// In the meantime, support comma-separated selectors by exploding them into an array.
-				$selectors = explode( ',', $block_type->attributes[ $attribute_name ]['selector'] );
-				// Add a bookmark to the first tag to be able to iterate over the selectors.
-				$block_reader->next_tag();
-				$block_reader->set_bookmark( 'iterate-selectors' );
-
-				// TODO: This shouldn't be needed when the `set_inner_html` function is ready.
-				// Store the parent tag and its attributes to be able to restore them later in the button.
-				// The button block has a wrapper while the paragraph and heading blocks don't.
-				if ( 'core/button' === $this->name ) {
-					$button_wrapper                 = $block_reader->get_tag();
-					$button_wrapper_attribute_names = $block_reader->get_attribute_names_with_prefix( '' );
-					$button_wrapper_attrs           = array();
-					foreach ( $button_wrapper_attribute_names as $name ) {
-						$button_wrapper_attrs[ $name ] = $block_reader->get_attribute( $name );
-					}
+				// Hardcode the selectors and processing until the HTML API is able to read CSS selectors and replace inner HTML.
+				// TODO: Use the HTML API instead.
+				if ( 'core/paragraph' === $this->name && 'content' === $attribute_name ) {
+					$selector = 'p';
 				}
-
-				foreach ( $selectors as $selector ) {
-					// If the parent tag, or any of its children, matches the selector, replace the HTML.
-					if ( strcasecmp( $block_reader->get_tag( $selector ), $selector ) === 0 || $block_reader->next_tag(
-						array(
-							'tag_name' => $selector,
-						)
-					) ) {
-						$block_reader->release_bookmark( 'iterate-selectors' );
-
-						// TODO: Use `set_inner_html` method whenever it's ready in the HTML API.
-						// Until then, it is hardcoded for the paragraph, heading, and button blocks.
-						// Store the tag and its attributes to be able to restore them later.
-						$selector_attribute_names = $block_reader->get_attribute_names_with_prefix( '' );
-						$selector_attrs           = array();
-						foreach ( $selector_attribute_names as $name ) {
-							$selector_attrs[ $name ] = $block_reader->get_attribute( $name );
-						}
-						$selector_markup = "<$selector>" . wp_kses_post( $source_value ) . "</$selector>";
-						$amended_content = new WP_HTML_Tag_Processor( $selector_markup );
-						$amended_content->next_tag();
-						foreach ( $selector_attrs as $attribute_key => $attribute_value ) {
-							$amended_content->set_attribute( $attribute_key, $attribute_value );
-						}
-						if ( 'core/paragraph' === $this->name || 'core/heading' === $this->name ) {
-							return $amended_content->get_updated_html();
-						}
-						if ( 'core/button' === $this->name ) {
-							$button_markup  = "<$button_wrapper>{$amended_content->get_updated_html()}</$button_wrapper>";
-							$amended_button = new WP_HTML_Tag_Processor( $button_markup );
-							$amended_button->next_tag();
-							foreach ( $button_wrapper_attrs as $attribute_key => $attribute_value ) {
-								$amended_button->set_attribute( $attribute_key, $attribute_value );
-							}
-							return $amended_button->get_updated_html();
-						}
+				if ( 'core/heading' === $this->name && 'content' === $attribute_name ) {
+					$selector = 'h[1-6]';
+				}
+				if ( 'core/button' === $this->name && 'text' === $attribute_name ) {
+					// Check if it is a <button> or <a> tag.
+					if ( preg_match( '/<button[^>]*>.*?<\/button>/', $block_content ) ) {
+						$selector = 'button';
 					} else {
-						$block_reader->seek( 'iterate-selectors' );
+						$selector = 'a';
 					}
 				}
-				$block_reader->release_bookmark( 'iterate-selectors' );
-				return $block_content;
+				if ( empty( $selector ) ) {
+					return $block_content;
+				}
+				$pattern = '/(<' . $selector . '[^>]*>).*?(<\/' . $selector . '>)/i';
+				return preg_replace( $pattern, '$1' . wp_kses_post( $source_value ) . '$2', $block_content );
 
 			case 'attribute':
 				$amended_content = new WP_HTML_Tag_Processor( $block_content );
@@ -408,13 +367,10 @@ class WP_Block {
 				}
 				$amended_content->set_attribute( $block_type->attributes[ $attribute_name ]['attribute'], $source_value );
 				return $amended_content->get_updated_html();
-				break;
 
 			default:
 				return $block_content;
-				break;
 		}
-		return;
 	}
 
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index c5f1e0699f..2c46c49274 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-58297';
+$wp_version = '6.6-alpha-58298';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.