[reporting-services] How do I set the visibility of a text box in SSRS using an expression?

Twood, Visibility expression is the expressions you write on how you want the "visibility" to behave. So, if you would want to hide or show the textbox, you want to write this:

=IIf((CountRows("ScannerStatisticsData")=0),True,False)

This means, if the dataset is 0, you want to hide the textbox.