Select by element types
The ability to select elements by type would be really useful and add a powerful functionality.
At the moment you can only select manually or select all.
A good example would be selecting all message flows on a diagram.
Once selected they could then be formatted to a light colour reduce the confusion that they can create on a busy diagram. They could be highlighted in a bright colour, or even hidden by setting to the background colour.
This can be achieved manually but a 'select by type' feature would make it so much easier.