Support for target attribute for links

[jochenwezel]

There is a need for implementation of the target attribut for links

Given is a common real-world scenario like this

<a href="http://example.com/" target="_blank">Hello, world!</a>

Currently supported syntax style in CommonMark.Net is at maximum:

[link](url "title")

http://stackoverflow.com/questions/4425198/markdown-target-blank already suggests several possible solutions for the different (common) markup versions.

As of above article, the most probably answer might be one of these syntax variants:

Maybe too simple solution ;-)

[link](url "title" "_blank")

With Markdown-2.5.2, you can use this:

[link](url){:target="_blank"}

Some projects use this style of extended attribution: {[attr]="[prop]"}

[link](url){target="_blank"}

Kramdown/standard common mark

[link](url){:target="_blank"}

https://talk.commonmark.org/t/multimarkdown-link-and-reference-image-attributes/1916
http://fletcher.github.io/MultiMarkdown-5/syntax.html#linkandimageattributes
https://talk.commonmark.org/t/links-with-attributes-like-target-class-etc/2246

After reading the specs and many discussion threads, I'd suggest following the [attr]="[prop]" system and keeping backwards compatibility to today's title definition:

[link](url "title")
[link](url title="title")
[link](url "title" target="_blank")
[link](url target="_blank" "title")
[link](url title="title" target="_blank")
[link](url "title" target="_blank" class="footer")
[link](url title="title" target="_blank" class="footer")

Everything additional must follow the [attr]="[prop]" standard,
everything else must be in quotation marks and represents the title attribute,
everything else is invalid.

[Knagis]

It seems that there is a PR pending in the specification: commonmark/commonmark-spec#105

If that PR would be merged, then that would mean that CommonMark.NET would also implement the attributes in the way it specifies.

[Knagis]

Closing until the spec is updated.