May user-friendly link names be empty?

[Sean Conner]

It was thus said that the Great codesoap at mailbox.org once stated:
> Hi Alex,
> thanks for your response! Unfortunately your answer still leaves me
> uncertain. Here you say, that trailing whitespace is illegal, if there
> is no link name:
> 
> > The user friendly link name is optional, however if it is present
> > then the whitespace after the url is mandatory as well.  In other words,
> > the URL is mandatory, and you either have no link name and no space
> > after the URL or a link name and mandatory space(s) after the URL.
> 
> The regular expression you suggest here, however, allows trailing
> whitespace, even if there is no link name:
> 
> > > a) ^=>[ \t]*([^ \t]+)(?:$|[ \t]+([^ \t].*)$)
> > > b) ^=>[ \t]*([^ \t]+)(?:$|[ \t]+([^ \t]?.*?)$)
> > I believe the latter (option b) would be correct.  I would remove the
> > final "[^ \t]?" and simplify it down to this:
> >     ^=>[ \t]*([^ \t]+)(?:$|[ \t]+(.*)$)
> 
> Do you have a link to an authoritative source upon which your knowledge
> on the matter is based? I wrote my initial mail on the topic, because
> I'm looking for an authoritative answer rather than an opinion.

  The two sources I know of are the one you already quoted (section 5.4.2 of
gemini://gemini.circumlunar.space/docs/specification.gmi) and a proposed BNF
for the revised specification
(https://gitlab.com/gemini-specification/gemini-text/-/issues/7).  

  Both leave the impression that (where spaces are replaced by '_'):

	=>gemini://example.com_

would not be allowed, but as with the real world, you may have to be a bit
lenient with the input (especially if it's user generated).  Also note that
as of now, the official spec allows both spaces (0x20) and tabs (0x09) to be
"whitespace", whereas the BNF only allowd spaces (0x20).  

  -spc