Changeset 2163 for draft-ietf-httpbis/latest

Timestamp:

25/01/13 13:29:05 (10 years ago)

Author:

fielding@…

Message:

reduce Accept-Language priority to a note about how some recipients treat the list as ordered and how user agents adjust to that by sending both distinct qvalues and list them in descending order; addresses #428

Location:

draft-ietf-httpbis/latest

Files:

• p2-semantics.html (modified) (1 diff)
• p2-semantics.xml (modified) (1 diff)

draft-ietf-httpbis/latest/p2-semantics.html

@@ -2005 +2005 @@
       </p>
       <div id="rfc.figure.u.33"></div><pre class="text">  Accept-Language: da, en-gb;q=0.8, en;q=0.7
-</pre><p id="rfc.section.5.3.5.p.5">would mean: "I prefer Danish, but will accept British English and other types of English". If no quality values are assigned
-         or multiple language tags have been assigned the same quality, the same-weighted languages are listed in descending order
-         of priority. Additional discussion of language priority lists can be found in <a href="http://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>.
-      </p>
-      <p id="rfc.section.5.3.5.p.6">For matching, <a href="http://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements. The
+</pre><p id="rfc.section.5.3.5.p.5">would mean: "I prefer Danish, but will accept British English and other types of English".</p>
+      <p id="rfc.section.5.3.5.p.6">Note that some recipients treat the order in which language tags are listed as an indication of descending priority, particularly
+         for tags that are assigned equal quality values (no value is the same as q=1). However, this behavior cannot be relied upon.
+         For consistency and to maximize interoperability, many user agents assign each language tag a unique quality value while also
+         listing them in order of decreasing quality. Additional discussion of language priority lists can be found in <a href="http://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>.
+      </p>
+      <p id="rfc.section.5.3.5.p.7">For matching, <a href="http://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements. The
          "Basic Filtering" scheme (<a href="#RFC4647" id="rfc.xref.RFC4647.4"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a>) is identical to the matching scheme that was previously defined for HTTP in <a href="http://tools.ietf.org/html/rfc2616#section-14.4">Section 14.4</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
       </p>
-      <p id="rfc.section.5.3.5.p.7">It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic
+      <p id="rfc.section.5.3.5.p.8">It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic
          preferences of the user in every request (<a href="#fingerprinting" title="Browser Fingerprinting">Section&nbsp;9.6</a>).
       </p>
-      <p id="rfc.section.5.3.5.p.8">Since intelligibility is highly dependent on the individual user, user agents need to allow user control over the linguistic
+      <p id="rfc.section.5.3.5.p.9">Since intelligibility is highly dependent on the individual user, user agents need to allow user control over the linguistic
          preference. A user agent that does not provide such control to the user <em class="bcp14">MUST NOT</em> send an Accept-Language header field.
       </p>
-      <div class="note" id="rfc.section.5.3.5.p.9"> 
+      <div class="note" id="rfc.section.5.3.5.p.10"> 
          <p> <b>Note:</b> User agents ought to provide guidance to users when setting a preference, since users are rarely familiar with the details
             of language matching as described above. For example, users might assume that on selecting "en-gb", they will be served any

draft-ietf-httpbis/latest/p2-semantics.xml

@@ -2331 +2331 @@
 <t>
    would mean: "I prefer Danish, but will accept British English and
-   other types of English". If no quality values are assigned or multiple
-   language tags have been assigned the same quality, the same-weighted
-   languages are listed in descending order of priority.
+   other types of English".
+</t>
+<t>
+   Note that some recipients treat the order in which language tags are listed
+   as an indication of descending priority, particularly for tags that are
+   assigned equal quality values (no value is the same as q=1). However, this
+   behavior cannot be relied upon. For consistency and to maximize
+   interoperability, many user agents assign each language tag a unique
+   quality value while also listing them in order of decreasing quality.
    Additional discussion of language priority lists can be found in
    <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>.