In this part of the Rough Notes, Mike Taulty discusses the linked RichTextBoxes in Silverlight 5.
Source: Mike Taulty's Blog
You’ll find a new class in the Silverlight 5 beta framework called the RichTextBoxOverflow – this is a really simple but really clever idea in that you can set up a RichTextBox and then you can tell it to overflow any content that doesn’t fit into that textbox into a RichTextBoxOverflow.