With read-only grids in a model-driven app, we're able to change the filter XML for the grid from Javascript using the setFilterXml() function. With a two-tier Editable grids, this appears to still work for the parent grid data.
let gridContext= formContext.getControl("grid_StateTotals");
gridContext.setFilterXml(newFetchXML);
But how do I filter the records on the child grids (subgrids)? Is there a way to access the individual subgrids to set the filter XML?