title: Construct string with multiple fonts
body: <p>I need to add strings coming from different RichTextBoxes with different fonts into one RichTextBox retaining the original fonts (more typically sometime I get XML  format where fonts for substrings is defined.)</p>
  
  <p>Is there a way of constructing this string in memory and then simply puting it in a RichTextBox? If not, is there any other way?</p>