1 <h2 id="ChromeSetting">Chrome settings</h2> 2 3 <p> 4 The <code>ChromeSetting</code> prototype provides a common set of functions 5 (<code>get()</code>, <code>set()</code>, and <code>clear()</code>) as 6 well as an event publisher (<code>onChange</code>) for settings of the 7 Chrome browser. The <a href="proxy.html#overview-examples">proxy settings 8 examples</a> demonstrate how these functions are intended to be used. 9 </p> 10 11 <h3 id="ChromeSetting-lifecycle">Scope and life cycle</h3> 12 13 <p> 14 Chrome distinguishes between three different scopes of browser settings: 15 <dl> 16 <dt><code>regular</code></dt> 17 <dd>Settings set in the <code>regular</code> scope apply to regular 18 browser windows and are inherited by incognito windows if they are not 19 overwritten. These settings are stored to disk and remain in place until 20 they are cleared by the governing extension, or the governing extension is 21 disabled or uninstalled.</dd> 22 23 <dt><code>incognito_persistent</code></dt> 24 <dd>Settings set in the <code>incognito_persistent</code> scope apply only 25 to incognito windows. For these, they override <code>regular</code> 26 settings. These settings are stored to disk and remain in place until 27 they are cleared by the governing extension, or the governing extension is 28 disabled or uninstalled.</dd> 29 30 <dt><code>incognito_session_only</code></dt> 31 <dd>Settings set in the <code>incognito_session_only</code> scope apply only 32 to incognito windows. For these, they override <code>regular</code> and 33 <code>incognito_session_only</code> settings. These settings are not 34 stored to disk and are cleared when the last incognito window is closed. They 35 can only be set when at least one incognito window is open.</dd> 36 37 </dl> 38 </p> 39 40 <h3 id="ChromeSetting-precedence">Precedence</h3> 41 42 <p> 43 Chrome manages settings on different layers. The following list describes the 44 layers that may influence the effective settings, in increasing order of 45 precedence. 46 <ol> 47 <li>System settings provided by the operating system</li> 48 <li>Command-line parameters</li> 49 <li>Settings provided by extensions</li> 50 <li>Policies</li> 51 </ol> 52 </p> 53 54 <p> 55 As the list implies, policies might overrule any changes that you specify with 56 your extension. You can use the <code>get()</code> function to determine whether 57 your extension is capable of providing a setting or whether this setting would 58 be overridden. 59 </p> 60 61 <p> 62 As discussed above, Chrome allows using different settings for regular 63 windows and incognito windows. The following example illustrates the behavior. 64 Assume that no policy overrides the settings and that an extension can set 65 settings for regular windows <b>(R)</b> and settings for incognito windows 66 <b>(I)</b>. 67 </p> 68 69 <p> 70 <ul> 71 <li>If only <b>(R)</b> is set, these settings are effective for both 72 regular and incognito windows.</li> 73 <li>If only <b>(I)</b> is set, these settings are effective for only 74 incognito windows. Regular windows use the settings determined by the lower 75 layers (command-line options and system settings).</li> 76 <li>If both <b>(R)</b> and <b>(I)</b> are set, the respective settings are 77 used for regular and incognito windows.</li> 78 </ul> 79 </p> 80 81 <p> 82 If two or more extensions want to set the same setting to different values, 83 the extension installed most recently takes precedence over the other 84 extensions. If the most recently installed extension sets only <b>(I)</b>, the 85 settings of regular windows can be defined by previously installed extensions. 86 </p> 87 88 <p> 89 The <em>effective</em> value of a setting is the one that results from 90 considering the precedence rules. It is used by Chrome. 91 <p> 92
