It isn't just sci-fi geeks who get into discussions of continuity and canonicity.
Check out
this Wikipedia entry. There you'll find how the last moments of the 80's television show
St. Elsewhere imply that the primary timeline of the show (featuring a hospital with lots of doctor drama, a la
ER) occurred in the imagination of one of the characters, an autistic boy who also imagined himself in the primary timeline as an autistic boy, with his "real-life" father as one of the doctors.
However, because there were crossovers of characters between that show and other shows, and because those shows had additional crossovers, you can quickly wind up with a six-degrees-of-Kevin-Bacon thing where the following shows all have a single "shared universe".
Someone even devoted a website to TV crossovers with a large section on the universes specifically.
AFTERMASH
The Andy Griffith Show
Ally
Ally McBeal
Arrested Development
The Beat
Becker
Beverly Hills Buntz
Bob
The Bob Newhart Show
Boston Legal
Boston Public
Buddies
Can't Hurry Love
Caroline In The City
Cheers
Chicago Hope
Civil Wars
Coach
Conviction
Cop Rock
COPS
Cosby
The Danny Thomas Show
Deadline
The Dick Van Dyke Show
The Drew Carey Show
Early Edition
Ellen
Everybody Loves Raymond
The Famous Teddy Z
Frasier
Friends
The Geena Davis Show
Gideon's Crossing
Gomer Pyle, U.S.M.C.
Grace Under Fire
High Society
Hill Street Blues
Home Improvement
Homicide: Life On The Street
Hope And Gloria
I Dream Of Jeannie
I Love Lucy
In Plain Sight
Ink
It's Gary Shandling's Show
Joey
The Joey Bishop Show
The John Larroquette Show
The King Of Queens
L.A. Law
Law And Order
Law And Order: Criminal Intent
Law And Order: Special Victims Unit
Law And Order: Trial By Jury
The Lone Gunmen
Love And War
Mad About You
Make Room For Daddy
Make Room For Granddaddy
Martial Law
M*A*S*H
Mayberry R.F.D.
Millennium
Murphy Brown
N.Y.P.D. Blue
The Nanny
New York Undercover
Newhart
Nick And Hillary
Norm/The Norm Show
Oz
Picket Fences
The Practice
Private Secretary
Public Morals
St. Elsewhere
Seinfeld
The Single Guy
Sons Of Thunder
Soul Man
Strange Luck
Tattingers
These Friends Of Mine
Thunder Alley
The Tortellis
Trapper John, M.D.
Walker, Texas Ranger
The White Shadow
Wings
The X-Files
However, I decided to check the reference at the site against Trek. Trek is placed in "Group 10" (not the St. Elsewhere group, but one featuring the Knight Rider universe of all things) based on a name-drop homage in Team Knight Rider regarding a character named Jackson Roykirk (creator of the Nomad probe in an episode of TOS).
This is far too vague to make for a decent connection. Further, the telemovie Knight Rider 2000 (which has as much claim of continuity as TKR, if not more, if only because someone actually
saw KR2000) features a James Doohan cameo with explicit reference to his portrayal of Scotty on television.
So, tenuous connections or not, it is at least of interest that such questions are clearly being asked of mainstream television. That way it's not just the sci-fi, soap opera, and Sherlock Holmes fans
previously mentioned.
(Hat tip: MinutiaeMan of Flare, whose term "St. Elsewhere Moment" set me to Googling.)
