You can leverage apache's mod_negotiation module. This way you can use the full range of negotiation capabilities the module offers, including your own preferences for the content type (e,g, "I really want to deliver application/xhtml+xml, unless the client very much prefers something else"). basic solution:

• AddHandler type-map .var

  içerikleri gibi olan bir. htaccess dosyası oluşturmak
• create a file foo.var with

  URI: foo
  
  URI: foo.php/html
  Content-type: text/html; qs=0.7
  
  URI: foo.php/xhtml
  Content-type: application/xhtml+xml; qs=0.8

  as contents
• create a file foo.php with

  <?php
  echo 'selected type: ', substr($_SERVER['PATH_INFO'], 1);

  as contents.
• istek http://localhost/whatever/foo.var

For this to work you need mod_negotiation enabled, the appropriate AllowOverride privileges for AddHandler and AcceptPathInfo not being disabled for $_SERVER['PATH_INFO'].
With my Firefox sending "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8" and the example .var map the result is "selected type: xhtml".
You can use other "tweaks" to get rid of PATH_INFO or the need to request foo.var, but the basic concept is: let mod_negotiation redirect the request to your php script in a way that the script can "read" the selected content-type.

So, does anyone know of a tried and tested piece of PHP code to select

Benim kütüphaneden küçük parçası:

function getBestSupportedMimeType($mimeTypes = null) {
    // Values will be stored in this array
    $AcceptTypes = Array ();

    // Accept header is case insensitive, and whitespace isn’t important
    $accept = strtolower(str_replace(' ', '', $_SERVER['HTTP_ACCEPT']));
    // divide it into parts in the place of a ","
    $accept = explode(',', $accept);
    foreach ($accept as $a) {
        // the default quality is 1.
        $q = 1;
        // check if there is a different quality
        if (strpos($a, ';q=')) {
            // divide "mime/type;q=X" into two parts: "mime/type" i "X"
            list($a, $q) = explode(';q=', $a);
        }
        // mime-type $a is accepted with the quality $q
        // WARNING: $q == 0 means, that mime-type isn’t supported!
        $AcceptTypes[$a] = $q;
    }
    arsort($AcceptTypes);

    // if no parameter was passed, just return parsed data
    if (!$mimeTypes) return $AcceptTypes;

    $mimeTypes = array_map('strtolower', (array)$mimeTypes);

    // let’s check our supported types:
    foreach ($AcceptTypes as $mime => $q) {
       if ($q && in_array($mime, $mimeTypes)) return $mime;
    }
    // no mime-type found
    return null;
}

örnek kullanım:

$mime = getBestSupportedMimeType(Array ('application/xhtml+xml', 'text/html'));

Armut :: HTTP 1.4.1 bir yöntemi vardır string negotiateMimeType( array $supported, string $default)

<?php
require 'HTTP.php';

foreach(
  array(
    'text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5',
    'text/*;q=0.3, text/html;q=0.8, application/xhtml+xml;q=0.7, */*;q=0.2',
    'text/*;q=0.3, text/html;q=0.7, */*;q=0.8',
    'text/*, application/xhtml+xml',
    'text/html, application/xhtml+xml'
  ) as $testheader) {  
  $_SERVER['HTTP_ACCEPT'] = $testheader;

  $http = new HTTP;
  echo $testheader, ' -> ',
    $http->negotiateMimeType( array('application/xhtml+xml', 'text/html'), 'application/xhtml+xml'),
    "\n";
}

prints

text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, /;q=0.5 -> application/xhtml+xml
text/*;q=0.3, text/html;q=0.8, application/xhtml+xml;q=0.7, */*;q=0.2 -> text/html
text/*;q=0.3, text/html;q=0.7, */*;q=0.8 -> application/xhtml+xml
text/*, application/xhtml+xml -> application/xhtml+xml
text/html, application/xhtml+xml -> text/html

Sadece kayıt için, Negotiation içerik müzakere ile başa çıkmak için saf bir PHP uygulamasıdır.

http://www.dev-archive.net/articles/xhtml.html#content-negotiation Perl ile yazılmış, ama açıkça ortaya koydu ve sadece bazı if / else ve regex oluşur. PHP için taşıma Önemsiz olmalıdır.