How to: Add Comments to Class Diagrams (Class Designer)
You can use comment shapes to annotate class diagrams. A comment shape has one property, Text, into which you can type text. Comment shapes exist only on the diagram surface and not in code.
A comment resides on the class diagram view in Class Designer; if you open a second class diagram onto the same project, comments you created in the first view are not visible. If you delete a diagram, all the comments it contained are also deleted.
You can resize a comment shape but you cannot change other aspects of its appearance, such as its background color, font, or font size.
To add a comment
Drag a comment from the Class Designer Toolbox onto the class diagram.
Click in the new comment shape on the diagram and type the text you want.