In the book (UML with Visual Studio.net), I couldn't find any details about how to add constraints to the message or operations in sequence diagram.

I tried two ways to add constraints to the message or operations.

1. Drag and drop constraint to the sequence diagram, but I couldn't find way to link this constraint to the message arrow line;

2. I went to the message prosperities, from there I added a constraint, but could not present in the diagram. I also could not find in the C# code generated from Visio.

Please give me the right procedures to add constraints to the message or operations. It will be much better if you can offer a sample.