It is not uncommon for a view creator to want to make it easy for a user to select one node and add all connected nodes of a particular element type to the view. This allows the view creator to keep the view simpler and faster but give their users a way to drill into more detail. This article will explain how to do this.
Here is a view of "Lorem Ipsum" nodes. Each can have connections to other elements in the city. Expanding we can add all or some of these connections, let's say that only the connections to "Somethings" are desired.
We could stop here (with a regular Expand button) but that's a lot of clicks for an end user to use, and perhaps we don't want them to be able to see some of the other connections.
Instead we'll give the Lorem Ipsum elements an Expand Custom control. This is from the settings Cog > Controls > Scroll down to the Lorem Ipsum element type > + > Expand Custom
This adds the Expand Custom control which we now simply need to click to edit and set element type to expand to "Something"
Optionally the label and icon be changed as well. These are what show up on the right had detail panel.
Now a user can click a single button and immediately add all the connected elements of the chosen type to the view!