[aguahombre]

In this jurisdiction, doubles are generally not alertable unless they are quite strange. A
penalty double where the whole world expects it it to be some form of takeout is supposed to be alerted, but even then if someone never heard of negative doubles how can we expect them to know their bidding is strange?

The negative double of a 1H overcall, if it denies spades, is considered alertable.

Other doubles, while still within the norm, seem to fall into a grey area not properly addressed, IMO. I chose this "changing regs" forum to bring one situation up, but who knows where it really belongs.

1m (1S) X (2S)
P (P) X.....This second double is the one I refer to. We choose to apply "When in doubt..." and alert this second double. We are not in doubt about what the alert regulations say; but, we do have doubt that the opponents understand OUR treatment and we believe they might well need this information before the auction is over.

This second double shows more strength than the first; but other than still having 4 hearts is still unclear as to where the auction should go. 2NT, instead, would show extra distribution rather than high card strength and bring diamonds into the picture.

We believe that this second double SHOULD be deemed alertable. Do you?

Somewhat related to disclosure or non-disclosure of "do something" doubles or action doubles, but not the same since we have more negative inferences.

[mikestar13]

I don't have an answer to this but it appears to be a special case of a general question: "To what extent should negative inferences be alerted? In absence of the 2NT alternative, the second double means "I still want you to do whatever my original double asked you to do.", implying but not guaranteeing extra values (basic bridge logic). In that case, the second double would not be alertable if the first one isn't.

[barmar]

To answer the more general question at the start of your post, ACBL's alerting regulation expects players to be familiar with common treatments used by our members in "standard" bidding, so that they don't have to enumerate all the possibilities in the regulation. So it effectly assumes that there's no player who is unfamiliar with negative doubles, responsive doubles, and other common doubles used primarily for takeout.

Since the regulation is describe in general terms, there are many situations that are hard to classify. That's where the rule "when in doubt, alert" comes in.