The start drawing nodes lets you select a function which gets added as a draw handler. This means you can draw into the viewport without a modal operator.
Name: The name of the node
Function: The function that should be run to draw into the viewport
Draw Type: If you’re drawing 3D elements into the 3D view you should use 3D. If you’re only drawing on top of the rest of the interface use 2D. If you want to draw behind the nodes into a node editor use Backdrop.
Space: The space type you want to draw into
