From 09a5cdda633b6e7bb807437cf29c46d068efa643 Mon Sep 17 00:00:00 2001
From: alstjr7375 <alstjr7375@daum.net>
Date: Fri, 8 Apr 2022 09:00:50 +0900
Subject: [PATCH] Doc: Add Preference

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+# Preference
+
+<!-- markdown-toc start - Don't edit this section. Run M-x markdown-toc-refresh-toc -->
+**Table of Contents**
+
+- [Basics](#basics)
+- [User Config](#user-config)
+- [Using with User Custom CSS](#using-with-user-custom-css)
+- [Related Source file](#related-source-file)
+
+<!-- markdown-toc end -->
+
+## Basics
+**Related Docs**
+- [Firefox Source Docs: libpref](https://firefox-source-docs.mozilla.org/modules/libpref/index.html)
+
+**Key/Value**
+- Key:
+  - Pref name
+  - Type: 8-bit string
+  - Convention is to use a dotted segmented form (Ex. `browser.cache.disk.enable`)
+- Value:
+  - Type: bool, 32-bit ints, 8-bit C string
+  - When you need an float, use a string. (Ex. `general.smoothScroll.currentVelocityWeighting`: `"0.25"`)
+
+**Main Purpose**
+- Feature enable/disable flags (Ex. `xpinstall.signatures.required`).
+- User preferences (Ex. things set from `about:preferences`)
+- Internal application parameters (Ex. `javascript.options.mem.nursery.max_kb`).
+- Application data (Ex. `browser.onboarding.tour.onboarding-tour-addons.completed`, `services.sync.clients.lastSync`).
+- Things that might need locking in an enterprise installation.
+
+## User Config
+**Related Docs**
+- [mozillaZine: Editing configuration](https://kb.mozillazine.org/Editing_configuration)
+- [Support Mozilla: How to fix preferences that won't save](https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save)
+- [Support Mozilla: Reset Firefox preferences to troubleshoot and fix problems](https://support.mozilla.org/en-US/kb/reset-preferences-fix-problems)
+- [UDN: A brief guide to Mozilla preferences](https://udn.realityripple.com/docs/Mozilla/Preferences/A_brief_guide_to_Mozilla_preferences)
+
+**Restrictions**
+
+It can be defined using only `user_pref()`.
+
+> User pref file syntax is slightly more restrictive than default pref file syntax. In user pref files `user_pref` definitions are allowed but `pref` and `sticky_pref` definitions are not, and attributes (such as `locked`) are not allowed.
+
+**`about:config`**
+
+It is written to `prefs.js` in a way that can be set by the GUI.
+
+- [Support Mozilla: Configuration Editor for Firefox](https://support.mozilla.org/en-US/kb/about-config-editor-firefox)
+
+**`prefs.js`**
+
+It exists in the profile directory, and is used to store settings that are changed from *defaults* or when users added *new settings*.
+
+In general, Do NOT edit `prefs.js` directly.
+
+- [mozillaZine: Prefs.js file](https://kb.mozillazine.org/Prefs.js_file)
+
+**`user.js`**
+- [mozillaZine: User.js file](https://kb.mozillazine.org/User.js_file)
+
+**Example**
+
+```javascript
+// user.js
+user_pref("browser.cache.disk.enable", false);                      // Bool
+user_pref("layout.css.prefers-color-scheme.content-override", 3);   // Int
+user_pref("general.smoothScroll.currentVelocityWeighting", "0.12"); // String
+```
+
+## Using with User Custom CSS
+**Related Docs**
+- [MDN: @supports](https://developer.mozilla.org/en-US/docs/Web/CSS/@supports)
+- [UDN: `CSS -moz-bool-pref() @supports function`](https://udn.realityripple.com/docs/Mozilla/Gecko/Chrome/CSS/-moz-bool-pref)
+
+**Restrictions**
+
+`@supports` change in CSS is not detected in real time. (Only start time)
+
+So a restart is required, and if the mozilla need real time changes, are using `@media` to handle it.
+
+If project only use pure CSS, we cannot add `@media rules`.
+
+- [Bug 1267890 - Support detecting bool preferences in chrome stylesheets](https://bugzilla.mozilla.org/show_bug.cgi?id=1267890)
+- [Bug 1698132 - Improve caching behaviour of -moz-bool-pref](https://bugzilla.mozilla.org/show_bug.cgi?id=1698132)
+
+**Example**
+
+Test each case by turning on/off the following settings.
+- `userChrome.navBar.red`
+- `userChrome.navBar.margin`
+
+```css
+/* userChrome.css */
+
+/* 1. If config is true */
+@supports -moz-bool-pref("userChrome.navBar.red") {
+  #nav-bar {
+    background-color: red !important;
+  }
+}
+
+/* 2. When any one of the config is true */
+@supports -moz-bool-pref("userChrome.navBar.red") or -moz-bool-pref("userChrome.navBar.margin") {
+  #nav-bar {
+    background-color: red !important;
+    margin-block: 20px;
+  }
+}
+
+/* 3. Multiple configs must all be satisfied */
+@supports -moz-bool-pref("userChrome.navBar.red") and -moz-bool-pref("userChrome.navBar.margin") {
+  #nav-bar {
+    background-color: red !important;
+    margin-block: 20px;
+  }
+}
+
+/* 4. 3's Other version */
+@supports -moz-bool-pref("userChrome.navBar.red") {
+  @supports -moz-bool-pref("userChrome.navBar.margin") {
+    #nav-bar {
+      background-color: red !important;
+      margin-block: 20px;
+    }
+  }
+}
+
+/* 5. If not exist or false */
+@supports not -moz-bool-pref("userChrome.navBar.red") {
+  #nav-bar {
+    background-color: blue !important;
+  }
+}
+```
+
+## Related Source file
+
+- https://github.com/mozilla/gecko-dev/blob/master/modules/libpref/parser/src/lib.rs
+- https://github.com/mozilla/gecko-dev/blob/master/extensions/pref/autoconfig/src/prefcalls.js