remap_file_lines (LineCache)

    # File lib/linecache.rb, line 226
      def remap_file_lines(from_file, to_file, range, start)
        range = (range..range) if range.is_a?(Fixnum)
        to_file = from_file unless to_file
        if @@file2file_remap_lines[to_file]
          # FIXME: need to check for overwriting ranges: whether
          # they intersect or one encompasses another.
          @@file2file_remap_lines[to_file] << [from_file, range, start]
        else
          @@file2file_remap_lines[to_file]  = [[from_file, range, start]]
        end
      end