From the ACBL's (
SAYC booklet, revised January, 2006:
Quote
OVERVIEW
The ACBL Standard American Yellow Card (SAYC) was created to be the required system to be used in a Standard Yellow Card event. The object was to provide a simple, modern method that will lead to a good, solid understanding in a partnership when both players have read this booklet.
Because this system was to be used by each pair, the game was free of a wide variety of possibly complex systems. There was no necessity to Alert or ask questions since everyone was playing the same method.
When play began on the Internet, players needing a quick way to establish the method to be used in a relatively casual partnership adopted the SAYC. It is also used by players who meet at the partnership desk a few minutes before the game starts.
Players may still exercise bridge judgment, such as opening a four-card major in third seat. SAYC “normally five-card majors” approach can withstand an occasional deviation.
CHOICES
While there are no choices in the present day SAYC, except for an SAYC event in which everyone must play the method as written, a pair could use the SAYC as a base and make one or two modifications. If you do make a modification or two in an open game, you should announce that fact to the opponents – if they think you are playing straight SAYC and they know SAYC, they would not know about your modifications.
There is room for an awful lot of variation in the context of
any basic system. As a matter of fact, SAYC is itself a variant of "Standard American". Bridge World Standard is another. Some writers, at least, have begun to refer to "Modern American" - another variant, although I suppose folks could debate whether it's a variant of "Standard American" or of "2/1 Game Force" and indeed whether the latter isn't itself a variant of "Standard American".
Years ago, NBOs would regulate systems. They would say "you can play Standard American, or Acol, or Precision, or ..., but not REGRES, or Moscito, or Joe's Homegrown Convention Collage". With all the variants that began to appear in supposedly standard systems, they gave up, and now regulate conventions, not systems. Even conventions have variants, though, which is why most SOs tell you that "explaining" a bid by naming a convention is not adequate disclosure. I would extend the principle to naming system. "SAYC" is only accurate if you play what's in the booklet, with no variations. "SAYC with extras" is probably okay.
As I understand it the custioms, if not the regulations, governing online bridge require an alert of anything that isn't SAYC. So unless there is a regulation to this effect referring to a specific version of SAYC other than the one in the booklet, I would alert anything that differs from the booklet version (or the specified version, if different) of SAYC.
Heh. A while back, my partner and I decided to try adding the game forcing 2/1 response to our card, which had been a fairly simple "standard american" card. When we did that, we - okay, I

- neglected to change the "Basic System" line at the top of the card to "2/1". Note that we hadn't added anything else normally considered part of 2/1. No Forcing NT, no inverted minors, no weak jump shifts, none of that stuff. One of the very good local players became upset with us - she said that not changing the basic system wording was misleading - she stopped shy of "deliberately" - and unfair. So we changed it to 2/1 GF, although I was sorely tempted to write "I don't know what to call it".
I had another partner who, when I was introduced to her, proudly said "I play SAYC!" I said "Good, then you play Jacoby 2NT." "Jacoby 2NT?" she said, "What's that?" I played with her for two or three years and we never did play that convention.