Want to use the TQRExprBuilder

Hi, I want to use the TQRExprBuilder in order to let the user pf my software
define his own expressions. I dont want to program my own Expression-
builder. I can create an instance and show it by doing

  uses qrexpbld;

  with tqrexprbuilder.create (self) do
  try
    Show
  finally
    free
  end;

but how can i assign datasources, and how can i get the builded
expression and set a default value at start?

Pleas mail me the answer! thanks -
Carsten Willems