Re: [ietf-822] "--" first in lines to indicate start of signature

Hector Santos <hsantos@isdg.net> Mon, 04 January 2016 19:23 UTC

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Date: Mon, 04 Jan 2016 14:23:21 -0500
From: Hector Santos <hsantos@isdg.net>
Organization: Santronics Software, Inc.
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To: Russ Allbery <eagle@eyrie.org>, "Murray S. Kucherawy" <superuser@gmail.com>
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Cc: ietf-822@ietf.org, Jacob Palme <jpalme@dsv.su.se>
Subject: Re: [ietf-822] "--" first in lines to indicate start of signature
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Hi Russ,

On 1/2/2016 6:38 PM, Russ Allbery wrote:> "Murray S. Kucherawy" 
<superuser@gmail.com> writes:
>
>> What other uses of "--" on a line by itself are there?  The only thing I
>> can think of is ASCII art.

I've written ASCII/ANSI/VT100 drivers and I don't recall a 
relationship other than some early body/text delimiter (ideal when you 
parse/read from the bottom, i.e. first delimiter encounter when 
reading up).

> Some people use it as a break between several thoughts.  This has probably
> grown since Markdown started using three hyphens to indicate a horizontal
> rule.  The distinction between two hyphens and three hyphens is the sort
> of thing that people don't always get right.

As I recall it, there was a "stripping war" and people tried to hide 
their tags using different identifiers.  QWK was a popular mail reader 
and it used something like, if I recall the format:

  ...
   X  QWK brag line where X was an extended "block-looking" character.

and Sparky did it so that it didn't get recognized and stripped. QWK 
format didn't want to get involved any Fidonet "regulation." 
Overall, mailers can do what they want. A reader or mailer was going 
to add its tag no matter what so it was not uncommon to see a bunch of 
"tear/tag" lines lumped together.

Much of the IETF stuff came from Fidonet where we didn't have a HEADER 
block.  We had kludge lines (Control A lines) that can appear anywhere 
in the payload.  That was one of the beauties of going to a more 
flexible, text-structured RFC822 format where increasing hardware 
speeds made it more feasible.   The Tear line and well as the Origin 
line were important body text delimiters since kludge lines were 
normally in the top and bottom of message.

   ^aPID
   ^aMSGID
   ^aREPLY
   ^aOther kludges

    body text

    --- tear line
     ^APath Line(s)
     ^aSeen-by Nodes line(s)

So mail processor developers can imagine what would be the logical 
varying coding techniques.  You can start at the bottom, get your 
seen-by and path lines, if any, and get to that first "tear line" or 
start at the top and get to the last one, etc.

> That being said, the more common problem is software recognizing -- at the
> start of a line as being the start of a signature even if it's followed by
> other text, which runs into issues with em-dashes as represented in ASCII.

I don't like the idea of trying to standardize a "-- " tag although 
this character sequence seems to be popular among "some" IETF users, 
but not outside.  As you said, other formats such as "--- " also exist 
and you have other variations as well.   There should be some 
guidelines I think for MUAs to consider or document, but not fix them 
to any set, if we can avoid it.

Why dashes?  Why not underscores? or Equal signs or in a modern 
extended character set world, Line (xC4) characters?

___ HLS
=== HLS
─── HLS

They all look "cool" and maybe using an extended code MAY help delimit 
it better, coding wise.

-- 
HLS