I'm fully with you.
Using hidden %System.whatever   Classes is as bad practice as using undocumented $zu(anynumber,  ,  , )

And if you also want to be sure that also the Method %New exists you my use

write $$$comMemberDefined(ClassName,"m","%New")

[just reading through %occReference.inc]

so you may use $$$comClassDefined(class)  for compile classes

or go for ^oddCOM(....)

You are right. The check for pure number got lost

if  +number=number  has to precede 

so the combined is  if  +number=number,number\1=+number

 (in my case 192.168.56.1), whereas one would need 71.174.62.16

This means you try to get information that is stored in your router's and/or firewall's  (NAT, DHCP,... ) routing/mapping table.
I'd assume you need to use some utility of your OS using $ZF(-1,...) $ZF(-2,...) to get the outside view of the inside server

This might work inquiring nslookup on a DNS server outside your NAT, ...  Though I never tried it

Thanks Ed! 
I just went through old DC post for half an hour+ to detect it. 

It's much better than my link to Facebook. 

Regards

just a guess:
with do content.MoveTo(content.Size - 1)   you are probably just between CR and LF 

Could you try do content.MoveTo(content.Size - 3)  just to make sure you a e before CRLF

I'm not sure how EOL is triggered
eventually also check returned success code

I don't see a call for  wnl()   
but ancient coding practices  would suggest its:  writenewline just that
and that's what it does without any other content.
though the remark is rater direct if interpreting feedback := line

// Should be smart as well: routines ending with write ! will create an empty feedback!

if you change wnl() ...
to
wnl()  quit
you just disable it to see if it plays a role at all    

to me this looks like your content had an extra $C(13,10) at the end.
It could help to  have the full content at hands. 
eg:
before  content.OutputToDevice()
set ck=content.Read()
set ^ck($i(^ck))=ck
do content.Rewind()

I expect  zwrite ^ck will show more than 3  lines
That would indicate that the source of trouble is on the input side. 
Some closing action ?   

You still have the option to create your own %ZLANGC00.int 
and make you own ZZEXIT to avoid the risky HALT
It's a miracle to me how HALT could survive from PDP-7 sn#103 at MGH and nobody touched it.
                           

indeed this is surprising.

but is this really:   do content.ReadLine(,,isEOL)

it should be a pass by reference to receive something back do content.ReadLine(,,.isEOL) 
with the <dot> in front of the variable