What are Open, Fetch, Close in Timeline View?

In PlanViz timeline view, executed operations can be in several states: Open, Fetch, Close, Pop, Sleep, Overhead

In a pop state, a physical operator is executed, the sleep state shows that an operation is currently not active but what do the Open, Fetch and Close states mean?

I can imagine that "Open"/"Close" means that a statement opens/clodes access to a table and "Fetch" means getting the data after having opened it.

Example (upper in Open state, lower in Fetch state):

However, first, I have not found any information in my books or in the web that confirms this assumption and second, I would like to know what exactly happens in these states technically.

Can anyone provide more detailed information about these three states?