What does it mean?
See idioms.thefreedictionary.com
by the by = Incidentally; on a side note; by the way.
An interjection meant to casually introduce or emphasize additional information in the conversation. Sometimes, though less commonly, written as "by the bye. By the by, I remembered where I left my keys, in case you were wondering. Beckett was an amazing playwright. There’s a lecture on his work tomorrow, by the by.
As a native speaker, I never say ‘by the by’. I don’t see any reason to use it when ‘by the way’ is more common and sounds better to my ears.
It seems you have been listening to and/or reading English of yesteryear. Why?
It’s from Alice in Wonderland, which is a classic. But yes, it’s an outdated phrase these days.
Okay Carlowf is reading Alice in Wonderland because it is a classic NOT because it is going to necessarily expand his English output (speaking is output, writing is output). Got it! I’m sure he’s enjoying the book.
I don’t know why …it is a book that I found on lingq …and it is a good book in my opinion…
Thanks for the roses, Carlowf. I’m glad you are enjoying the book. You might enjoy this http://blinkist.com/ resource. Most of the content is contemporary, up-to-date English.