README updates for extensions.

configure.py

@@ -65,7 +65,10 @@ def read_template_dir(directory):
         'stylesheet': open(f'{directory}/stylesheet.qss.in').read(),
         'icons': [],
     }
-    icon_data = load_json(f'{directory}/icons.json')
+    if os.path.exists(f'{directory}/icons.json'):
+        icon_data = load_json(f'{directory}/icons.json')
+    else:
+        icon_data = {}
     for file in glob.glob(f'{directory}/*.svg.in'):
         svg = open(file).read()
         name = os.path.splitext(os.path.splitext(os.path.basename(file))[0])[0]

extension/README.md

@@ -3,25 +3,152 @@ extensions
 
 Extensions enable the creation of stylesheets using the same, customizable themes of the original stylesheet. This both allows refining the generated stylesheet and supporting third-party Qt plugins/widgets.
 
-**TODO(ahuszagh)**
+Extensions are optionally added to the generated stylesheets, allowing you to extend existing stylesheets to support third-party plugins and optional features.
 
-- Describe stylesheet.qss.in
-- Describe icons.json
+Furthermore, this simplifies making local, application-specific changes, without having to deal with merge conflicts when fetching updates.
 
-Document this...
-
-# Current Extensions
+# Pre-Packaged Extensions
 
 **Advanced Docking System**
 
-**TODO(ahuszagh)** Add description and image
+This extension adds support for the [Advanced Docking System](https://github.com/githubuser0xFFFF/Qt-Advanced-Docking-System). This comes with styles for the dock manager to create a consistent theme between the main stylesheet and the docking system.
+
+In order to use this extension, configure with:
+
+```bash
+python configure.py --extensions=advanced-docking-system
+```
+
+And make sure to [disable](https://github.com/githubuser0xFFFF/Qt-Advanced-Docking-System/blob/master/doc/user-guide.md#disabling-the-internal-style-sheet) the internal stylesheet in the dock manager.
+
+<p align="center"><b>Linux</b></p>
+<figure>
+    <img 
+        alt="Advanced Docking System View 1"
+        src="/assets/advanced-docking-system1.png" 
+        title="AdvancedDockingSystem1" 
+    />
+</figure>
+
+<p align="center"><b>Linux</b></p>
+<figure>
+    <img 
+        alt="Advanced Docking System View 2"
+        src="/assets/advanced-docking-system2.png" 
+        title="AdvancedDockingSystem2" 
+    />
+</figure>
+
+<p align="center"><b>Linux</b></p>
+<figure>
+    <img 
+        alt="Advanced Docking System View 3"
+        src="/assets/advanced-docking-system3.png" 
+        title="AdvancedDockingSystem3" 
+    />
+</figure>
+
+<p align="center"><b>Linux</b></p>
+<figure>
+    <img 
+        alt="Advanced Docking System View 4"
+        src="/assets/advanced-docking-system4.png" 
+        title="AdvancedDockingSystem4" 
+    />
+</figure>
 
 **QDockWidget Tooltips**
 
-Adds tooltips to QDockWidget's float and close buttons.
+This extension adds tooltips to QDockWidget's float and close buttons.
 
-**TODO(ahuszagh)** Add image
+In order to use this extension, configure with:
+
+```bash
+python configure.py --extensions=dock-tooltips
+```
+
+<p align="center"><b>Linux</b></p>
+<figure>
+    <img 
+        alt="Dock Tooltips"
+        src="/assets/dock-tooltips.png" 
+        title="DockTooltips" 
+    />
+</figure>
 
 # Creating Extensions
 
-**TODO(ahuszagh)** Document...
+Creating extensions extends the existing stylesheet configurations, and adds custom rules to the stylesheet, which can then be configured for all themes. This supports custom icons, rules, and more.
+
+Each extension is added as a folder in [extension](/extension), with a template stylesheet file named `stylesheet.qss.in`. Additional icons can be added as SVG template files (with the extension `svg.in`), and icon styling rules in `icons.json`.
+
+**Simple Example**
+
+For example, to add tooltips to a `QDockWidget`, create a `stylesheet.qss.in`  in the directory `extension/tooltips` with the following contents:
+
+```css
+QAbstractButton#qt_dockwidget_closebutton
+{
+    qproperty-toolTip: "Close";
+}
+
+QAbstractButton#qt_dockwidget_floatbutton
+{
+    qproperty-toolTip: "Detach";
+}
+```
+
+To build the stylesheet with the extension, run:
+
+```bash
+python configure.py --extensions=tooltips
+```
+
+**Icons Example**
+
+For a more complex example, let's consider a third-party extension of a `QPushButton` with the object name `customButton`, which has a configurable icon. First, create a directory named `extension/custom-button`.
+
+Next, let's create an SVG template for the icon, at `icon.svg.in`:
+
+```svg
+<svg width="405" height="290">
+  <g transform="scale(5)">
+    <rect fill="^0^" x="36" width="3" height="17"/>
+    <rect fill="^0^" x="66" y="29.75" height="2" width="15"/>
+  </g>
+</svg>
+```
+
+Here, `^0^` signifies index-based replacement, so we must define an entry in 
+`icons.json` to specify how we should do the replacement.
+
+```json
+{
+    "icon": {
+        "default": ["foreground"],
+        "hover": ["highlight"]
+    }
+}
+```
+
+Index-based replacement allows us to create more than 1 icon from a single template, with different colors. Here, this would create `icon.svg` with the theme's foreground color, and `icon_hover.svg` with the theme's highlight color.
+
+Next, we want to add the rules to use these icons in the stylesheet:
+
+```css
+QPushButton#customButton
+{
+    qproperty-icon: url(:/dark/icon.svg);
+}
+
+QPushButton#customButton:hover
+{
+    qproperty-icon: url(:/dark/icon_hover.svg);
+}
+```
+
+To build the stylesheet with the extension, run:
+
+```bash
+python configure.py --extensions=custom-button
+```

extension/dock-tooltips/icons.json

@@ -1,3 +0,0 @@
-// NOTE: This is a custom JSON file, where lines leading
-// with `//` are removed. No other comments are valid.
-{}