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docs/chrome_settings.md

+# Table of Contents
+
+
+
+# What is chrome://settings?
+
+Chrome (version 10 and above) uses WebUI settings by default for all platforms. Access it via the wrench menu ("Preferences" on Mac and Linux; "Options" on Windows and ChromeOS), or by typing chrome://settings into the address bar.
+
+One advantage of chrome://settings over platform-native dialogs is that it is shared by all platforms; therefore, it is easier to add new options UI and to keep all platforms in sync.
+
+Note that at the time of this writing, DOMUI is being renamed to WebUI. The two terms will be used interchangeably herein.
+
+# Moving parts
+
+## String resources
+
+Strings live in `chrome/app/generated_resources.grd`. There are several rules governing the format of strings:
+  * the **casing of button text** depends on the platform. If your string will be displayed on a button, you need to add it twice, in sentence case and title case. Follow examples inside `<if expr="pp_ifdef('use_titlecase')">` blocks. Do this even if your string is a single word because it may not be a single word in another locale.
+  * strings that are associated with form controls (buttons, checkboxes, dropdowns, etc.) should NOT have **trailing punctuation**. Standalone strings, such as sectional descriptive text, should have trailing punctuation.
+  * strings may be different between Google Chrome and chromium. If they differ only in **product name**, put them in `generated_resources.grd` and use product name placeholders; if they differ more substantially, use `chromium_strings.grd` and `google_chrome_strings.grd`.
+
+## WebUI Handlers
+
+The C++ WebUI handler classes for chrome://settings live in `chrome/browser/ui/webui/options/`. These objects both handle messages from and dispatch messages to the page. Each handler is a logical grouping of related functionality. Hence `ContentSettingsHandler` is both the delegate and controller of the content settings subpage.
+
+A handler sends a message to the page via `dom_ui_->CallJavascriptFunction()` and registers for messages from the page via `dom_ui_->RegisterMessageCallback()`.
+
+## HTML/CSS/JS
+
+The HTML, CSS, and JS resources live in `chrome/browser/resources/options`. They are compiled into one resource at compile time by grit, via `<link>`, `<src>` and `<include>` tags in `options.html`. There is no need to add new files to any `.gyp` file.
+
+Some things that are good to know:
+  * JS objects are bound to HTML nodes via `decorate()`.
+  * Javascript calls into C++ via `chrome.send`.
+  * Some automatic preference handling is provided in `preferences.js` and `pref_ui.js`.
+  * Strings defined in a WebUI handler are available via `localStrings.getString()` and friends.
+
+# Example: adding a simple pref
+
+Suppose you want to add a pref controlled by a **checkbox**.
+
+## 1. Getting UI approval
+
+Ask one of the UI leads where your option belongs. First point of contact should be Alex Ainslie <ainslie at chromium>.
+
+## 2. Adding Strings
+
+Add the string to `chrome/app/generated_resources.grd` near related strings. No trailing punctuation; sentence case.
+
+## 3. Changing WebUI Handler
+
+For simple prefs, the UI is kept in sync with the value automagically (see `CoreOptionsHandler`). Find the handler most closely relevant to your pref. The only action we need take here is to make the page aware of the new string. Locate the method in the handler called `GetLocalizedStrings` and look at its body for examples of `SetString` usage. The first parameter is the javascript name for the string.
+
+## 4. HTML/CSS/JS
+
+An example of the form a checkbox should take in html:
+
+```
+  <label class="checkbox">
+    <input id="clear-cookies-on-exit"
+        pref="profile.clear_site_data_on_exit" type="checkbox">
+    <span i18n-content="clearCookiesOnExit"></span>
+  </label>
+```
+
+Of note:
+  * the `checkbox` class allows us to style all checkboxes the same via CSS
+  * the class and ID are in dash-form
+  * the i18n-content value is in camelCase
+  * the pref attribute matches that which is defined in `chrome/common/pref_names.cc` and allows the prefs framework to automatically keep it in sync with the value in C++
+  * the `i18n-content` value matches the string we defined in the WebUI handler. The `textContent` of the `span` will automatically be set to the associated text.
+
+In this example, no additional JS or CSS are needed.