on DDoc macros: a small problem

[Charles Hixson]

I have, towards the start of my file:

  /** Macros:
  * Note = $(BR)$(BIG$(B$(GREEN  Note:)))
  * Todo = <br><font color=red><b>ToDo:</b> $0</font><br>
  * Em = $(B$(BLUE $0))
  * DoNotUse = $(B Do Not Use $0)
  */

Why do I need that DoNotUse macro to terminate the Em macro?  If I don't 
include it, the Em macro picks up the first line of the next 
documentation comment, and includes it as a part of itself.  I'm clearly 
doing something wrong, but I have no idea what.