If we use the following code to set the value of an extraction variable:

SetExtractedValue("TagIndex","button:0");

and try to use TagIndex in find expression to make it data driven, the test will fail for the click test step with the following information:

Failure Information: 
~~~~~~~~~~~~~~~
Unable to locate element. Details: Attempting to find [Html] element using 
Find logic 
 (Html): [TagIndex 'Exact' button:0] AND [TextContent 'Exact' Click Me!]

The strange thing is that this is a valid find expression and if it was not data driven the step will pass.