diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/class-wp-walker.php
--- a/wp/wp-includes/class-wp-walker.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/class-wp-walker.php	Tue Dec 15 13:49:49 2020 +0100
@@ -135,25 +135,23 @@
 		$id_field = $this->db_fields['id'];
 		$id       = $element->$id_field;
 
-		//display this element
+		// Display this element.
 		$this->has_children = ! empty( $children_elements[ $id ] );
 		if ( isset( $args[0] ) && is_array( $args[0] ) ) {
 			$args[0]['has_children'] = $this->has_children; // Back-compat.
 		}
 
-		$cb_args = array_merge( array( &$output, $element, $depth ), $args );
-		call_user_func_array( array( $this, 'start_el' ), $cb_args );
+		$this->start_el( $output, $element, $depth, ...array_values( $args ) );
 
-		// descend only when the depth is right and there are childrens for this element
-		if ( ( $max_depth == 0 || $max_depth > $depth + 1 ) && isset( $children_elements[ $id ] ) ) {
+		// Descend only when the depth is right and there are childrens for this element.
+		if ( ( 0 == $max_depth || $max_depth > $depth + 1 ) && isset( $children_elements[ $id ] ) ) {
 
 			foreach ( $children_elements[ $id ] as $child ) {
 
 				if ( ! isset( $newlevel ) ) {
 					$newlevel = true;
-					//start the child delimiter
-					$cb_args = array_merge( array( &$output, $depth ), $args );
-					call_user_func_array( array( $this, 'start_lvl' ), $cb_args );
+					// Start the child delimiter.
+					$this->start_lvl( $output, $depth, ...array_values( $args ) );
 				}
 				$this->display_element( $child, $children_elements, $max_depth, $depth + 1, $args, $output );
 			}
@@ -161,14 +159,12 @@
 		}
 
 		if ( isset( $newlevel ) && $newlevel ) {
-			//end the child delimiter
-			$cb_args = array_merge( array( &$output, $depth ), $args );
-			call_user_func_array( array( $this, 'end_lvl' ), $cb_args );
+			// End the child delimiter.
+			$this->end_lvl( $output, $depth, ...array_values( $args ) );
 		}
 
-		//end this element
-		$cb_args = array_merge( array( &$output, $element, $depth ), $args );
-		call_user_func_array( array( $this, 'end_el' ), $cb_args );
+		// End this element.
+		$this->end_el( $output, $element, $depth, ...array_values( $args ) );
 	}
 
 	/**
@@ -181,23 +177,25 @@
 	 * $max_depth > 0 specifies the number of display levels.
 	 *
 	 * @since 2.1.0
+	 * @since 5.3.0 Formalized the existing `...$args` parameter by adding it
+	 *              to the function signature.
 	 *
 	 * @param array $elements  An array of elements.
 	 * @param int   $max_depth The maximum hierarchical depth.
+	 * @param mixed ...$args   Optional additional arguments.
 	 * @return string The hierarchical item output.
 	 */
-	public function walk( $elements, $max_depth ) {
-		$args   = array_slice( func_get_args(), 2 );
+	public function walk( $elements, $max_depth, ...$args ) {
 		$output = '';
 
-		//invalid parameter or nothing to walk
+		// Invalid parameter or nothing to walk.
 		if ( $max_depth < -1 || empty( $elements ) ) {
 			return $output;
 		}
 
 		$parent_field = $this->db_fields['parent'];
 
-		// flat display
+		// Flat display.
 		if ( -1 == $max_depth ) {
 			$empty_array = array();
 			foreach ( $elements as $e ) {
@@ -250,7 +248,7 @@
 		 * If we are displaying all levels, and remaining children_elements is not empty,
 		 * then we got orphans, which should be displayed regardless.
 		 */
-		if ( ( $max_depth == 0 ) && count( $children_elements ) > 0 ) {
+		if ( ( 0 == $max_depth ) && count( $children_elements ) > 0 ) {
 			$empty_array = array();
 			foreach ( $children_elements as $orphans ) {
 				foreach ( $orphans as $op ) {
@@ -273,19 +271,21 @@
 	 * $max_depth > 0 specifies the number of display levels.
 	 *
 	 * @since 2.7.0
+	 * @since 5.3.0 Formalized the existing `...$args` parameter by adding it
+	 *              to the function signature.
 	 *
 	 * @param array $elements
 	 * @param int   $max_depth The maximum hierarchical depth.
-	 * @param int   $page_num The specific page number, beginning with 1.
+	 * @param int   $page_num  The specific page number, beginning with 1.
 	 * @param int   $per_page
+	 * @param mixed ...$args   Optional additional arguments.
 	 * @return string XHTML of the specified page of elements
 	 */
-	public function paged_walk( $elements, $max_depth, $page_num, $per_page ) {
+	public function paged_walk( $elements, $max_depth, $page_num, $per_page, ...$args ) {
 		if ( empty( $elements ) || $max_depth < -1 ) {
 			return '';
 		}
 
-		$args   = array_slice( func_get_args(), 4 );
 		$output = '';
 
 		$parent_field = $this->db_fields['parent'];
@@ -295,7 +295,7 @@
 			$total_top = count( $elements );
 		}
 		if ( $page_num < 1 || $per_page < 0 ) {
-			// No paging
+			// No paging.
 			$paging = false;
 			$start  = 0;
 			if ( -1 == $max_depth ) {
@@ -311,7 +311,7 @@
 			}
 		}
 
-		// flat display
+		// Flat display.
 		if ( -1 == $max_depth ) {
 			if ( ! empty( $args[0]['reverse_top_level'] ) ) {
 				$elements = array_reverse( $elements );
@@ -425,7 +425,7 @@
 	 * @since 2.7.0
 	 *
 	 * @param object $e
-	 * @param array $children_elements
+	 * @param array  $children_elements
 	 */
 	public function unset_children( $e, &$children_elements ) {
 		if ( ! $e || ! $children_elements ) {
@@ -444,4 +444,4 @@
 		unset( $children_elements[ $id ] );
 	}
 
-} // Walker
+}