2.1/user/src/com/google/gwt/user/UserAgent.gwt.xml

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<!-- Copyright 2007 Google Inc.                                             -->
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<!-- Defines the user.agent property and its provider function.             -->
<!--                                                                        -->
<!-- This module is typically inherited via com.google.gwt.user.User        -->
<!--                                                                        -->
<module>

  <!-- Browser-sensitive code should use the 'user.agent' property -->
  <define-property name="user.agent" values="ie6,ie8,gecko,gecko1_8,safari,opera"/>

  <property-provider name="user.agent"><![CDATA[
      var ua = navigator.userAgent.toLowerCase();
      var makeVersion = function(result) {
        return (parseInt(result[1]) * 1000) + parseInt(result[2]);
      };

      if (ua.indexOf("opera") != -1) {
        return "opera";
      } else if (ua.indexOf("webkit") != -1) {
        return "safari";
      } else if (ua.indexOf("msie") != -1) {
        if (document.documentMode >= 8) {
          return "ie8";
        } else {
          var result = /msie ([0-9]+)\.([0-9]+)/.exec(ua);
          if (result && result.length == 3) {
            var v = makeVersion(result);
            if (v >= 6000) {
              return "ie6";
            }
          }
        }
      } else if (ua.indexOf("gecko") != -1) {
        var result = /rv:([0-9]+)\.([0-9]+)/.exec(ua);
        if (result && result.length == 3) {
          if (makeVersion(result) >= 1008)
            return "gecko1_8";
          }
        return "gecko";
      }
      return "unknown";
  ]]></property-provider>

  <!-- Deferred binding to optimize JRE classes based on user agent. -->
  <inherits name="com.google.gwt.emul.EmulationWithUserAgent"/>
  <inherits name="com.google.gwt.core.CoreWithUserAgent"/>
</module>