code: def insert(text, offset)
           if !@text.nil?
              @text = @text[0, offset] + text.to_s + @text[offset, @text.length]
           else
              @text = text.to_s
           end
        end
docs: This method inserts a String into the existing text within a TextNode
   object. If the TextNode contains no text then it is simply set to the
   text passed in. If the offset specified is past the end of the nodes
   text then it is simply appended to the end.
  
   ==== Parameters
   text::    A String containing the text to be added.
   offset::  The numbers of characters from the first character to insert
             the new text at.