diff -r be944660c56a -r 3d72ae0968f4 wp/wp-includes/class-wp-block-styles-registry.php
--- a/wp/wp-includes/class-wp-block-styles-registry.php	Wed Sep 21 18:19:35 2022 +0200
+++ b/wp/wp-includes/class-wp-block-styles-registry.php	Tue Sep 27 16:37:53 2022 +0200
@@ -17,7 +17,8 @@
 	 * Registered block styles, as `$block_name => $block_style_name => $block_style_properties` multidimensional arrays.
 	 *
 	 * @since 5.3.0
-	 * @var array
+	 *
+	 * @var array[]
 	 */
 	private $registered_block_styles = array();
 
@@ -25,12 +26,13 @@
 	 * Container for the main instance of the class.
 	 *
 	 * @since 5.3.0
+	 *
 	 * @var WP_Block_Styles_Registry|null
 	 */
 	private static $instance = null;
 
 	/**
-	 * Registers a block style.
+	 * Registers a block style for the given block type.
 	 *
 	 * @since 5.3.0
 	 *
@@ -60,6 +62,15 @@
 			return false;
 		}
 
+		if ( str_contains( $style_properties['name'], ' ' ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Block style name must not contain any spaces.' ),
+				'5.9.0'
+			);
+			return false;
+		}
+
 		$block_style_name = $style_properties['name'];
 
 		if ( ! isset( $this->registered_block_styles[ $block_name ] ) ) {
@@ -71,7 +82,9 @@
 	}
 
 	/**
-	 * Unregisters a block style.
+	 * Unregisters a block style of the given block type.
+	 *
+	 * @since 5.3.0
 	 *
 	 * @param string $block_name       Block type name including namespace.
 	 * @param string $block_style_name Block style name.
@@ -94,7 +107,7 @@
 	}
 
 	/**
-	 * Retrieves an array containing the properties of a registered block style.
+	 * Retrieves the properties of a registered block style for the given block type.
 	 *
 	 * @since 5.3.0
 	 *
@@ -115,20 +128,19 @@
 	 *
 	 * @since 5.3.0
 	 *
-	 * @return array Array of arrays containing the registered block styles properties grouped per block,
-	 *               and per style.
+	 * @return array[] Array of arrays containing the registered block styles properties grouped by block type.
 	 */
 	public function get_all_registered() {
 		return $this->registered_block_styles;
 	}
 
 	/**
-	 * Retrieves registered block styles for a specific block.
+	 * Retrieves registered block styles for a specific block type.
 	 *
 	 * @since 5.3.0
 	 *
 	 * @param string $block_name Block type name including namespace.
-	 * @return array Array whose keys are block style names and whose value are block style properties.
+	 * @return array[] Array whose keys are block style names and whose values are block style properties.
 	 */
 	public function get_registered_styles_for_block( $block_name ) {
 		if ( isset( $this->registered_block_styles[ $block_name ] ) ) {
@@ -138,7 +150,7 @@
 	}
 
 	/**
-	 * Checks if a block style is registered.
+	 * Checks if a block style is registered for the given block type.
 	 *
 	 * @since 5.3.0
 	 *