Index: wp-includes/rewrite.php
===================================================================
--- wp-includes/rewrite.php	(revision 19736)
+++ wp-includes/rewrite.php	(working copy)
@@ -52,11 +52,19 @@
  *
  * @param string $name Name for permalink structure.
  * @param string $struct Permalink structure.
- * @param bool $with_front Prepend front base to permalink structure.
+ * @param array $args Optional configuration for building the rules from the permalink structure,
+ *     see {@link WP_Rewrite::add_permastruct()} for full details.
  */
-function add_permastruct( $name, $struct, $with_front = true, $ep_mask = EP_NONE ) {
+function add_permastruct( $name, $struct, $args = array() ) {
 	global $wp_rewrite;
-	return $wp_rewrite->add_permastruct( $name, $struct, $with_front, $ep_mask );
+
+	// backwards compatibility for the old parameters: $with_front and $ep_mask
+	if ( ! is_array( $args ) )
+		$args = array( 'with_front' => $args );
+	if ( func_num_args() == 4 )
+		$args['ep_mask'] = func_get_arg( 3 );
+
+	return $wp_rewrite->add_permastruct( $name, $struct, $args );
 }
 
 /**
@@ -993,7 +1001,7 @@
 			return false;
 
 		if ( isset($this->extra_permastructs[$name]) )
-			return $this->extra_permastructs[$name][0];
+			return $this->extra_permastructs[$name]['struct'];
 
 		return false;
 	}
@@ -1518,11 +1526,15 @@
 		$page_rewrite = apply_filters('page_rewrite_rules', $page_rewrite);
 
 		// Extra permastructs
-		foreach ( $this->extra_permastructs as $permastructname => $permastruct ) {
-			if ( is_array($permastruct) )
-				$rules = $this->generate_rewrite_rules($permastruct[0], $permastruct[1]);
-			else
-				$rules = $this->generate_rewrite_rules($permastruct, EP_NONE);
+		foreach ( $this->extra_permastructs as $permastructname => $struct ) {
+			if ( is_array( $struct ) ) {
+				if ( count( $struct ) == 2 )
+					$rules = $this->generate_rewrite_rules( $struct[0], $struct[1] );
+				else
+					$rules = $this->generate_rewrite_rules( $struct['struct'], $struct['ep_mask'], $struct['paged'], $struct['feed'], $struct['forcomments'], $struct['walk_dirs'], $struct['endpoints'] );
+			} else {
+				$rules = $this->generate_rewrite_rules( $struct );
+			}
 
 			$rules = apply_filters($permastructname . '_rewrite_rules', $rules);
 			if ( 'post_tag' == $permastructname )
@@ -1817,24 +1829,57 @@
 	}
 
 	/**
-	 * Add permalink structure.
+	 * Add a new permalink structure.
 	 *
-	 * These are added along with the extra rewrite rules that are merged to the
-	 * top.
+	 * A permalink structure (permastruct) is an abstract definition of a set of rewrite rules; it
+	 * is an easy way of expressing a set of regular expressions that rewrite to a set of query strings.
+	 * The new permastruct is added to the {@link WP_Rewrite::$extra_permastructs} array. When the
+	 * rewrite rules are built by {@link WP_Rewrite::rewrite_rules()} all of these extra permastructs
+	 * are passed to {@link WP_Rewrite::generate_rewrite_rules()} which transforms them into the
+	 * regular expressions that many love to hate.
 	 *
+	 * The $args parameter gives you control over how {@link WP_Rewrite::generate_rewrite_rules()}
+	 * works on the new permastruct.
+	 *
 	 * @since 2.5.0
 	 * @access public
 	 *
 	 * @param string $name Name for permalink structure.
-	 * @param string $struct Permalink structure.
-	 * @param bool $with_front Prepend front base to permalink structure.
+	 * @param string $struct Permalink structure (e.g. category/%category%)
+	 * @param array $args Optional configuration for building the rules from the permalink structure:
+	 *     - with_front (bool) - Should the structure be prepended with WP_Rewrite::$front? Default is true.
+	 *     - ep_mask (int) - Endpoint mask defining what endpoints are added to the structure. Default is EP_NONE.
+	 *     - paged (bool) - Should archive pagination rules be added for the structure? Default is true.
+	 *     - feed (bool) - Should feed rewrite rules be added for the structure? Default is true.
+	 *     - forcomments (bool) - Should the feed rules be a query for a comments feed? Default is false.
+	 *     - walk_dirs (bool) - Should the 'directories' making up the structure be walked over and rewrite
+	 *                          rules built for each in turn? Default is true.
+	 *     - endpoints (bool) - Should endpoints be applied to the generated rewrite rules? Default is true.
 	 */
-	function add_permastruct($name, $struct, $with_front = true, $ep_mask = EP_NONE) {
-		if ( $with_front )
+	function add_permastruct( $name, $struct, $args = array() ) {
+		// backwards compatibility for the old parameters: $with_front and $ep_mask
+		if ( ! is_array( $args ) )
+			$args = array( 'with_front' => $args );
+		if ( func_num_args() == 4 )
+			$args['ep_mask'] = func_get_arg( 3 );
+
+		$defaults = array(
+			'with_front' => true,
+			'ep_mask' => EP_NONE,
+			'paged' => true,
+			'feed' => true,
+			'forcomments' => false,
+			'walk_dirs' => true,
+			'endpoints' => true, // really necessary?
+		);
+		$args = wp_parse_args( $args, $defaults );
+		$args['struct'] = $struct;
+
+		if ( $args['with_front'] )
 			$struct = $this->front . $struct;
 		else
 			$struct = $this->root . $struct;
-		$this->extra_permastructs[$name] = array($struct, $ep_mask);
+		$this->extra_permastructs[ $name ] = $args;
 	}
 
 	/**