Ada Procedure Parameters That Use the Plus Sign

[NiGHTS <nights@unku.us>]

I recently stumbled across some Ada code that appends a plus sign in front of a parameter name of a function or procedure call. From the context it seems like it is doing a forced cast between two incompatible types. 

Here is one example I found in the AdaGtk demo create_tree_view.adb line 243:

Gtk_New (Tree, +Model);


My questions are:

1. What is this called? Is there a name for this?

2. What exactly is happening here?

3. Is it safe? Should it be avoided?

4. Is there another way to accomplish this without the use of '+' ?

5. Where can I find out more about this?


Thank you for your help.