should IP-Address-alikes be considered valid?

[shabble]

Are these intended behaviour? I haven't dug too hard into the referenced RFCs so it's possible they are valid, but ISTR there was previously a 'cannot start with a number' rule that was subsequently relaxed to allow some, but not exclusively, leading digits.

Following examples I think probably all(?) should actually be False?

In [38]: !pip freeze | grep fqdn
fqdn==1.5.1

In [39]: fqdn.FQDN('1').is_valid
Out[39]: False

In [40]: fqdn.FQDN('1', min_labels=1).is_valid
Out[40]: True

In [41]: fqdn.FQDN('127.0.0.1').is_valid
Out[41]: True

In [42]: fqdn.FQDN('127.thing.0.1').is_valid
Out[42]: True

In [43]: fqdn.FQDN('127.0.0.0.1').is_valid
Out[43]: True

I could convert those into tests in a PR if it does seem like a bug?

For my use it would ideally either accept a valid IP address (without a trailing FQ dot), or a valid hostname, but not something like 1.2.3.4.5, although separating valid IPs from invalid 'dotted numeric' inputs is something I can handle if it doesn't make sense here.

A quick poke around some of the docs, found in RFC1123, sec 2.1:

If a dotted-decimal number can be entered without such identifying delimiters, then a full syntactic check must be made, because a segment of a host domain name is now allowed to begin with a digit and could legally be entirely numeric (see Section 6.1.2.4). However, a valid host name can never have the dotted-decimal form #.#.#.#, since at least the highest-level component label will be alphabetic.