Server.format(_:for:)

The listed types carry the fields worth modelling — a Pane knows its id, its size, and what is running in it. tmux publishes hundreds more, and this reaches any of them without the library having to name each one first:

Ask for as many fields as you like in one template, separated by whatever the value cannot contain — a newline is the one separator to avoid, since a connection reads commands by line and refuses one.

• Returns: what tmux printed, minus the newline it ends every answer with, or nil when target no longer resolves.