Minor fix in mrlib/hierlist docs

collects/mrlib/scribblings/hierlist/compound-item.scrbl

@@ -47,7 +47,7 @@ Returns a list of all immediate items in the sub-list.}
 Shows or hides the items of this sub-list.}
 
 
-@defmethod[(is-open) boolean?]{
+@defmethod[(is-open?) boolean?]{
 
 Reports whether the items of this sub-list are visible.}
 

collects/mrlib/scribblings/hierlist/item.scrbl

@@ -42,4 +42,10 @@ list. This method is intended for use with an automatic test suite.}
 
 Gets/sets whether this item is allowed to be selected.}
 
+
+@defmethod[(get-parent) (or/c (is-a?/c hierarchical-list-compound-item<%>) #f)]{
+
+Returns the compound list item that contains the item or @racket[#f] if
+none exists.}
+
 }