check-names settings

[Mark Andrews]

	Labels start with a letter or digit.  Labels end with a
	letter or digit.  Letter, digit or hypen in the middle of
	the label.

	All labels meet the above with the exception of a mbox where
	second to last labels meet the above.

	A single period can also be used as a place marker.

	The rules are applied to the owner names of A, AAAA and
	MX records.
	NS and MX records rdata.
	IN-ADDR.ARPA and IP6.ARPA PTR records rdata.
	(I don't think I've missed any cases).

	Underscore was choosen for SRV records so that they would
	*not* clash with hostnames.

	Active directory similarly uses underscore to *not* clash
	with host names, gc uses a A record but as *all* the
	particiants in AD are *known* to cope it is not a problem.

	Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org