TaggedValues.GetAttribute

[qwerty]

I'm wondering what that might be. The help says

Returns the text of a single named property within a structured Tagged Value.
Parameters:
propName: String - the name of the property for which the text is being returned

Now, that does not make me much wiser. So I passed an arbitrary string, but anything but a null string results in

What's this?

Similarly for HasAttributes:

Returns True if the Tagged Value is a structured Tagged Value with one or more properties.

My tag is clearly inside a structure (it's from a BPMN Activity). But what are those properties?

q.

P.S. Seems I found out what those properties are.  Thanks to Google. So I guess the error message is just one of those "you did something wrong, stupid" ones.