referencing the Image Description (longdesc) extension from HTML core spec #49

Ref w3c/html#507 (comment)

This to me is not so much about the longdesc attribute as much as the format of the html5 spec in general. The decision was made ( which i agree with ) to modularize the HTML spec and reference extension specs from it.

The main difference i see here is that this takes the modularization a step further as this is just an attribute it seems a bit much, to need to got to and reference another document, just for an attribute. I would like to hear others opinions on the usability of this pattern.

There has been some pretty heated discussion in the issue already i highly recommend reading up on.