- From: Mark Nottingham <mnot@mnot.net>
- Date: Thu, 11 Dec 2008 10:54:51 +1100
- To: Roy T. Fielding <fielding@gbiv.com>
- Cc: Yves Lafon <ylafon@w3.org>, Julian Reschke <julian.reschke@gmx.de>, HTTP Working Group <ietf-http-wg@w3.org>
Right, OK; that's the subtle bit. Julian, make sense? On 11/12/2008, at 8:19 AM, Roy T. Fielding wrote: > On Dec 10, 2008, at 3:01 AM, Yves Lafon wrote: > >> On Wed, 10 Dec 2008, Julian Reschke wrote: >> >>> >>> Mark Nottingham wrote: >>>> ... >>>> <t>HTML4 also has a "rev" parameter for links that allows a >>>> link's relation to be reversed. The Link header >>>> has a "rev" parameter to allow the expression of these >>>> links in HTTP headers, but its use is not encouraged, >>>> due to the confusion this mechanism causes as well as >>>> conflicting interpretations among HTML versions.</t> >>>> ... >>> >>> OK, it seems I'm missing something here. Could somebody explain to >>> me, what the conflicting interpretations are, and which we prefer >>> (and why?)? >>> >>> HTML2 (<http://tools.ietf.org/html/rfc1866#section-5.7.3>): >>> >>> REL >>> The REL attribute gives the relationship(s) described by >>> the hyperlink. The value is a whitespace separated list >>> of relationship names. The semantics of link >>> relationships are not specified in this document. >>> >>> REV >>> same as the REL attribute, but the semantics of the >>> relationship are in the reverse direction. A link from A >>> to B with REL="X" expresses the same relationship as a >>> link from B to A with REV="X". An anchor may have both >>> REL and REV attributes. >> >> In that case, it's not a reversed link, but still a normal forward >> link, but it expressed a reversed relationship. >> A: link rel="bigger than" B >> is the same relation as >> B: link rev="smaller than" A >> >> Same relation, but different links (and different authority >> claiming the relationship between both A and B). >> In the HTML4 example, it's reverse and forward links, so the links >> are supposed equivalent, so not only the relation is equivalent, >> but also the link. >> I prefer far more the "relationship equivalence" as defined in HTML2. > > Yep. The HTML2 definition is correct but easily misunderstood because > "expresses the same relationship" does not mean "is the same link". > What it should have said is that rev reverses the relationship > semantics, > e.g., rev=made is equivalent to rel=creator. Both define a link > from A to B. > > ....Roy > -- Mark Nottingham http://www.mnot.net/
Received on Wednesday, 10 December 2008 23:55:34 UTC