Recent UI changes mean that command output may be displayed in more than one window.
The long term goal was bug 657595 (and to a certain extent bug 659301) where commands would output some JSON (or similar) and some sort of a 'mime-type' and GCLI would then find a way to convert that type to DOM.
So commands wanting to do rich output would need to register 2 things, the command, and the converter. The win being that converters could be shared, and that we could resurrect command output (for uses like history, etc)
However we need the ability to have document-free output without significant work, so this bug is for a small hack that solves the 'arbitrary document' problem, without solving the bigger problem.
Fixed with the closing of bug 720641