module Hpricot::Container::Trav

It doesn't return location object even if self is location object.
+filter+ returns an node.

inner nodes are examined.
If given block returns true, corresponding node is retained and
If given block returns false, corresponding node is dropped.
+filter+ yields each node except top node.

loc.filter {|descendant_loc| predicate } -> node
node.filter {|descendant_node| predicate } -> node

+filter+ rebuilds the tree without some components.

def filter(&block)
  subst = {}
  each_child_with_index {|descendant, i|
    if yield descendant
      if descendant.elem?
        subst[i] = descendant.filter(&block)
      else
        subst[i] = descendant
      end
    else
      subst[i] = nil
    end
  }
  to_node.subst_subnode(subst)
end