Select a tool from the drop down above the viewport.
Left Click to use the selected tool.
Try double clicking at any point before/during/after use.
When a double click is detected, the viewport size changes and an info message is displayed just below the viewport.
Note that a double click is permitted during any phase of annotation creation and it does not change the state of the annotation.
Double clicking an arrow annotation to edit its text stops the event from bubbling up.