Would anyone consider implementing attribute lists ?

[velsa]

Those greatly extend markdown functionality via single markup element.
For more details, see this extension: Attribute Lists

[NoelDavies]

That's not really part of markdown though, and it doesn't really conform to how markdown looks or feels? :/ I've personally never seen it before.

Where are you using it?

[joshbruce]

Agree with @NoelDavies (also see #956). Not part of markdown and I think goes beyond the purpose of markdown:

Plain, human-readable, text converted to HTML; or, other output.

Closing.