Syntax question: Which grid rows are expanded?

SmartClient 9.0:

In a ListGrid where canExpandRecords = true, is there a quick way to gather an array of all records that are currently expanded?

At the moment, I'm trying to loop through listgrid.data(), and checking listGrid.isExpanded(record), but the performance is pretty poor.

It seems like there ought to be a listGrid.getExpanded() function, but I'm not seeing anything like that in the documentation.

Thanks!