SmartyPants and dashes

[Virgil Arrington]

Please bear with me as I am just a user and, by no means, a developer. 
However, I've noticed some inconsistent behavior among different 
implementations of SmartyPants when it comes to en-dashes and em-dashes.

**1. Calibre 2.7*

*When I recently uploaded a Markdown source file to Calibre and selected 
its "Smarten punctuation" feature, it converted a double-hyphen "--" 
into an em-dash, and a triple hyphen "---" into an en-dash. This 
behavior was the opposite that I have come to expect using both LaTeX 
and ReText, my default Markdown editor.

I reported the matter as a Calibre bug, but received a response saying 
that the Calibre behavior was based on the official SmartyPants source 
code, which states as follows:

"The string, with each instance of "--" translated to an em-dash HTML 
entity, and each "---" translated to an en-dash HTML entity. Two reasons 
why: First, unlike the en- and em-dash syntax supported by 
EducateDashesOldSchool(), it's compatible with existing entries written 
before SmartyPants 1.1, back when "--" was only used for em-dashes. 
Second, em-dashes are more common than en-dashes, and so it sort of 
makes sense that the shortcut should be shorter to type. (Thanks to 
Aaron Swartz for the idea.)*"

*Confused by this, I tested two other methods of using SmartyPants, and 
received inconsistent results.

*2**. Python Markdown v2.5.1*

I use ReText as my Markdown editor. It uses the Smartypants extension 
that is provided with Python Markdown v2.5.1. It translates "--" as an 
endash and "---" as an emdash, the *opposite* as Calibre. Below is the 
translation table found at 
https://pythonhosted.org/Markdown/extensions/smarty.html

ASCII symbol 	Replacements 	HTML Entities 	Substitution Keys
|'| 	' ' 	|‘| |’| 	|'left-single-quote'|, 
|'right-single-quote'|
|"| 	" " 	|“| |”| 	|'left-double-quote'|, 
|'right-double-quote'|
|<< >>| 	« » 	|«| |»| 	|'left-angle-quote'|, 
|'right-angle-quote'|
|...| 	... 	|…| 	|'ellipsis'|
|--| 	-- 	|–| 	|'ndash'|
|---| 	--- 	|—| 	|'mdash'|


At the bottom of the Python/SmartyPants extension page is the following:

"SmartyPants extension is based on the original SmartyPants 
implementation by John Gruber. Please read it's documentation 
<http://daringfireball.net/projects/smartypants/> for details."

Based on this, I went to Gruber's page and got yet more inconsistency.

*3. SmartyPants by John Gruber.*

At Gruber's SmartyPants page, 
(http://daringfireball.net/projects/smartypants/) the following is found:

"SmartyPants can perform the following transformations:

  * Straight quotes ( " and ' ) into "curly" quote HTML entities
  * Backticks-style quotes (|``like this''|) into "curly" quote HTML
    entities
  * *Dashes ("**|--|**" and "**|---|**") into en- and em-dash entities *
  * **Three consecutive dots ("|...|") into an ellipsis entity"

Based on the order of the dashes listed, it would appear as if Gruber is 
suggesting that "--" would turn into an en-dash, and "---" into an 
em-dash (consistent with ReText, but not with Calibre). But, if I use 
Gruber's online Dingus translator 
(http://daringfireball.net/projects/markdown/dingus), I get yet a third 
variation of the conversion. Gruber's online translator converts "--" 
into an em-dash (as does Calibre) /but/ it turns "---" into an em-dash 
plus a hyphen (no en-dash).

There appears to be either confusion or disagreement in the 
Markdown/SmartyPants world as to how to create typographic dashes. Is 
there any way that the developers can come together on this very small 
part of the Markdown world?

Virgil
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