Having the player set a fragment param (like #storyPlayer=v0) on the doc will enable us to do three things:

(1) make runtime changes (e.g. minor UI tweaks) when in a player
(2) load (or not) the viewer integration conditionally, without work from the publisher
(3) have at least some way of getting basic analytics (if we eventually load cache URLs, then we'll know e.g. when the document was loaded and can attribute that to a load in the player... Maybe at a later date we can message things from the player to the doc for additional signals)