handle whole-row validation

[githorse]

I can add validation to specific editing components. But say I have a validation that needs to run on an entire row -- for instance, I might want to check if the row I'm editing is (now) an exact duplicate of another row. If the row fails validation, I need to show an error message somewhere (preferably right below the row, inside the grid, I would think), and disable the save button. Does anyone have any suggestions on how to make this work?