I'm using yEd 3.9.2. With BPMN, how do I include things in a sub-process?

Question

I'm trying to draw a BPMN process flow. I want to include a sub-process. I dragged a sub-process to the working area. I've tried dragging other tasks, etc. on top of it. However, they aren't included in the sub-process. In other words, when I select and move the sub-process, they are left behind to fend for themselves. 

I see the yEd grouping capability but that isn't BPMN. I'm trying to stick to BPMN only symbols.

Answer 1

A subprocess BPMN node is a representative for several other BPMN nodes and corresponds to a folder node, i.e. you cannot add child nodes to it. However, exactly as folder nodes can be "opened" to be group nodes, clicking the subprocess node's "+" sign will convert it to a task node that corresponds to a group node. In this state it is possible to add child nodes to the node.