custom attributes

I want to add some custom attributes (e.g. user_id) to my grid, so that I can read them with grid.getRowAttribute(row,"user_id"); .

If I load the data from an xml File I can add these attributes. But how do I add these attributes when I fill the grid with json?

thanks hibbert

Here is example of adding custom attribute to the row in JSON:

rows:[ { id:"1001", custom_attribute:"value", data:[ "100", "150", "clue", "12.99", "1", "05/01/1998"] },
also the attributes can be added by the API:
grid.setRowAttribute(“unique_rowid”,“some”,“new value”);