nsIFind in Firefox 1.5

 Find some text in the current context. The implementation is
 responsible for performing the find and highlighting the text.

 @param aPatText     The text to search for.
 @param aSearchRange A Range specifying domain of search.
 @param aStartPoint  A Range specifying search start point.
                     If not collapsed, we'll start from
                     end (forward) or start (backward).
                     May be null; if so, we'll start at the start
                     (forward) or end (back) of aSearchRange.
 @param aEndPoint    A Range specifying search end point.
                     If not collapsed, we'll end at
                     end (forward) or start (backward).
                     May be null; if so, we'll end at the end
                     (forward) or start (back) of aSearchRange.
 @retval             A range spanning the match that was found (or null).