Define a 'length' attribute to Link constructs.
Retracted -- jumped the gun, obsolote now I've written PaceLinkEnclosure
Related and Conflicting Proposals
Decouple 'length' from PaceEnclosuresAndPix
Even if PaceEnclosuresAndPix does not get into the spec, a 'length' attribute for <link> elements will still be useful, especially considering that an 'enclosure' or 'attachment' relationship could be added to the IANA Link Relationships Register after Atom goes 1.0.
Add to 3.5 a new section.
=== 3.5.x "length" attribute === This attribute's value MUST be an integer number which gives the expected size in bytes of the representation received by dereferencing the URI in the value of the href attribute. Link constructs MAY have a length attribute.