[Zope] rendering DTML stored in property sheets ?

[chas]

Here's a silly thing that's always niggled me : 

How do you get Zope to render the DTML that is 
stored in properties of a ZClass ? 

eg. Consider you have a ZClass with a string 
    property called 'my_property'

    In an instance of this ZClass, you set the 
    value of 'my_property' to "Hello <dtml-var x>"
    where x might be a string, integer, image etc

    Now, if a DTML method were to call <dtml-var my_property>,
    it would display "Hello <dtml-var x>"
    How can we get the DTML to be executed too, so that it
    displays "Hello [value of x]". Is there any easy method
    other than splitting this up into different fields ? 

Apologies if this is such a trivial thing. It's
escaped me for ages.

chas