Detect selection when going from Grid Summary to Detail

Imagine a table with columns: id, product_id, product_category, quantity.

Imagine also a grid is defined on this with group_by set on product_category and the grid set to start in Summary mode.

So say there are 2 distinct product_category entries (“Books” and “Music”) showing in Summary, if you click “Books”, is there an easy way to determine this was clicked? Clearly there are no Ajax events configuration for Summary.

Nested grid…can work? U can trigger a program in its on load event in that grid