Run time Expression QR

Hi,
What I have got is a simple report form, based on the nature of the report
which is determined from a list of report types the program creates an
instance of the report form.

If predefined (user) expression is to assign to a TQrExpr control at
runtime, how would this can be achieved at run time
TQrExpr .Expression := 'Expression'?

any help is appreciate it

regards