Row expansion is controlled with expandedRows property. The column that has the expander element requires expander property to be enabled. Optional rowExpand and rowCollapse events are available as callbacks.
Expanded rows can either be an array of row data or when dataKey is present, an object whose keys are strings referring to the identifier of the row data and values are booleans to represent the expansion state e.g. {'1004': true}. The dataKey alternative is more performant for large amounts of data.