Header Rows This collection contains the top set of rows; it is used by the topLeftCells and columnHeaders panels. By default, this collection contains one row.
Scrollable Rows This collection contains the main set of rows; it is used by the cells and rowHeaders panels. By default, this collection contains no rows. It is populated when you set the grid's itemsSource property.
Footer Rows This collection contains the bottom set of rows; it is used by the bottomLeftCells and columnFooters panels. By default, this collection is empty.
The three row collections are RowCollection objects, which extend regular arrays. You may add or remove rows by adding or removing Row objects from these arrays. In most cases, however, you won't add or remove scrollable rows, since the grid does that automatically when you set the itemsSource property.
For example, the grid below has an extra fixed row, automatically-generated scrollable rows, and a footer row: