This property value is being kept in sync with a number of items in the System.Windows.Controls.Grid.RowDefinitions collection.
If a number of items in the System.Windows.Controls.Grid.RowDefinitions collection has been changed then the value of the RowCount property is updated automatically.
If a value of the RowCount property is changed directly, then items will be added or removed to/from the end of System.Windows.Controls.Grid.RowDefinitions collection until its number becomes equal to the new RowCount value.