That's a good question. Even within internal Cisco documents I have not found one that will list exactly what can be used there. But after some experimentation of my own, it looked like it will take any abbreviation used for the "well-known port numbers" 0 through 1023, such as pop3, smtp, tftp, and so on. You are correct that it will also take the format of tcp/110, and udp/110 should work as well. I hope that will help.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...