What problem does this feature solve?

in the treemap options I can drag the chart completely out of view. Having looked through the docs I can not see a suitable option for this. I want roam mode to be available but I want to limit the range it can travel.

What does the proposed API look like?

Add a limit option to the roam feature to prevent the treemap going out of range

something like

roamBoundary: {
height: 
width: 
}