Where is the property for the text in a text object?

Blender version: 2.72

I would like to create a driver to change the text displayed in a text object.

For all the drivers I have created in the past I have found the property I want to drive, right clicked, selected the “add a [single] driver” from the menu and taken it from there. But I can’t find the property of a text object that is the actual text it displays. I have found the properties for the spacing, the alignment, the geometry, etc. so i think I am looking in the place where it ought to be. But I can’t find it.

Does it exist? If it does, can someone please point me at it.

Apologies in advance if I’m just being blind.

You can see the actual text in the Datablocks section of the outliner.
There is not the option to add a driver


Looks like it can’t be done then. Thank you.