A lot of arguing about whether, "Continue" or "Extend" is correct phraseology. Doesn't seem to matter to me...both are equally vague and mean about the same thing.
At PAO, I've always heard "Extend". It's a common request. It can be nerve-wracking trying to figure out the controllers intent, as right downwind for 31, the most common place to be, runs straight into NUQ (Moffett). Unless you're local, you may not know that there's an LoA that gives up a chunk of NUQ's airspace to PAO almost permanently. Shoreline Amphitheater defines this line. If you're not local and get the instruction very close to the charted Delta, it may be very confusing. To make matters worse, the same LoA allows "extensions into Moffett" at the mutual agreement of the two towers. Which is confusing, because there's already a standing extension into Moffett. What "extensions into Moffett" means is all the way to Hangar One, which is solidly inside the pattern at KNUQ. Usually, you'll be told about "extensions into Moffett" when being asked to "Extend downwind" if they are in place.
The confusing part is coming close to Shoreline without acknowledged extensions on an extend instruction and basically being boxed in with no good outs. Worse, PAO gets busy enough that interjecting a timely question can become impossible. (This is especially true when being asked to extend, of course.) Even more confusing is that "I'll call you base" is also a common instruction that may or may not be included with "extend downwind". (So, by not saying that, do you mean I should turn base at my discretion?) Often the instructions come abeam the numbers, with what looks like plenty of time. So, you may not worry too much about it yet or ask for clarification, because it doesn't seem to matter. Then...that invisible wall starts looming and you're hoping some instruction comes soon in the flurry of instructions being sent out as the controller attempts to keep the very busy pattern in line.
Eh, I don't know where I'm going with this other than to indicate it's a common issue.