title: Shared Column Headers in XamDataGrid via GUI at runtime
body: <p>How does the user change the columns in a XamDataGrid such that it sets the ColumnSpan and/or RowSpan properties?  I know how to do this programatically, but I can't seem to figure out how to do it via the keyboard and mouse at runtime.  Are there any options I need to set on the grid in order for this to work?</p>