Gtk.TreeDragSource.prototype.row_draggable

function row_draggable(path:Gtk.TreePath):Boolean {
    // Gjs wrapper for gtk_tree_drag_source_row_draggable()
}

Asks the Gtk.TreeDragSource whether a particular row can be used as the source of a DND operation. If the source doesn't implement this interface, the row is assumed draggable.