quality degradation factor for the features attribute, see
         section 6.4 of [2].
   As an example, if a variant list contains the variant description

     {"paper.html.en" 0.7 {type text/html} {language fr}}

   and if the request contains the Accept- headers

     Accept: text/html:q=1.0, */*:q=0.8
     Accept-Language: en;q=1.0, fr;q=0.5

   the remote variant selection algorithm will compute an overall
   quality for the variant as follows:

     {"paper.html.fr" 0.7 {type text/html} {language fr}}
                       |           |                 |
                       |           |                 |
                       V           V                 V
             round5 ( 0.7   *     1.0        *      0.5 ) = 0.35000





 
RFC 2296                     HTTP RVSA/1.0                    March 1998


   With the above Accept- headers, the complete variant list

     {"paper.html.en" 0.9 {type text/html} {language en}},
     {"paper.html.fr" 0.7 {type text/html} {language fr}},
     {"paper.ps.en"   1.0 {type application/postscript} {language en}}

   would yield the following computations:

            round5 ( qs  * qt  * qc  * ql  * qf  ) =   Q
                     ---   ---   ---   ---   ---     -------
      paper.html.en: 0.9 * 1.0 * 1.0 * 1.0 * 1.0   = 0.90000
      paper.html.fr: 0.7 * 1.0 * 1.0 * 0.5 * 1.0   = 0.35000
      paper.ps.en:   1.0 * 0.8 * 1.0 * 1.0 * 1.0   = 0.80000

3.4 Definite and speculative quality values

   A computed overall quality value can be either definite or
   speculative.  An overall quality value is definite if it was computed
   without using any wildcard characters '*' in the Accept- headers, and
   without the need to use the absence of a particular Accept- header.
   An overall quality value is speculative otherwise.

   As an example, in the previous section, the quality values of
   paper.html.en and paper.html.fr are definite, and the quality value
   of paper.ps.en is speculative because the type application/postscript
   was matched to the range */*.

   Definiteness can be defined more formally as follows.  An overall
   quality value Q is definite if the same quality value Q can be
   computed after the request message is changed in the following way:

       1. If an Accept, Accept-Charset, Accept-Language, or
          Accept-Features header is missing from the request, add this
          header with an empty field.

       2. Delete any media ranges containing a wildcard character '*'
          from the Accept header.  Delete any wildcard '*' from the
          Accept-Charset, Accept-Language, and Accept-Features headers.

   As another example, the overall quality factor for the variant

     {"blah.html" 1 {language en-gb} {features blebber [x y]}}

   is 1 and definite with the Accept- headers

     Accept-Language: en-gb, fr
     Accept-Features: blebber, x, !y, *





 
RFC 2296                     HTTP RVSA/1.0                    March 1998


   and

     Accept-Language: en, fr
     Accept-Features: blebber, x, *

   The overall quality factor is still 1, but speculative, with the
   Accept- headers

     Accept-language: en-gb, fr
     Accept-Features: blebber, !y, *

   and

     Accept-Language: fr, *
     Accept-Features: blebber, x, !y, *