By The Way Meaning

(conjunctive, speech act, idiomatic) Incidentally; a parenthetical statement not timely, central, or crucial to the topic at hand; foregone, passed by, something that has already happened.

Example: 1853, Herman Melville, Bartleby, the Scrivener, in Billy Budd, Sailor and Other Stories, New York: Penguin Books, 1968; reprint 1995 as Bartleby, ISBN 0 14 60.0012 9, p.2:
  [...] I had counted on a life-lease of the profits, whereas I only received those of a few short years. But this is by the way.
1918, W. B. Maxwell, chapter 7, The Mirror and the Lamp:
  â€œA very welcome, kind, useful present, that means to the parish. By the way, Hopkins, let this go no further. We don't want the tale running round that a rich person has arrived. Churchill, my dear fellow, we have such greedy sharks, and wolves in lamb's clothing. […]”
  His mother will be coming for dinner tomorrow, and, by the way, she volunteered to bring dessert.‎