Add "small" (extended) markdown style support

lib/src/models/documents/attribute.dart

@@ -19,6 +19,7 @@ class Attribute<T> {
   static final Map<String, Attribute> _registry = LinkedHashMap.of({
     Attribute.bold.key: Attribute.bold,
     Attribute.italic.key: Attribute.italic,
+    Attribute.small.key: Attribute.small,
     Attribute.underline.key: Attribute.underline,
     Attribute.strikeThrough.key: Attribute.strikeThrough,
     Attribute.font.key: Attribute.font,
@@ -43,6 +44,8 @@ class Attribute<T> {
 
   static final ItalicAttribute italic = ItalicAttribute();
 
+  static final SmallAttribute small = SmallAttribute();
+
   static final UnderlineAttribute underline = UnderlineAttribute();
 
   static final StrikeThroughAttribute strikeThrough = StrikeThroughAttribute();
@@ -82,6 +85,7 @@ class Attribute<T> {
   static final Set<String> inlineKeys = {
     Attribute.bold.key,
     Attribute.italic.key,
+    Attribute.small.key,
     Attribute.underline.key,
     Attribute.strikeThrough.key,
     Attribute.link.key,
@@ -217,6 +221,10 @@ class ItalicAttribute extends Attribute<bool> {
   ItalicAttribute() : super('italic', AttributeScope.INLINE, true);
 }
 
+class SmallAttribute extends Attribute<bool> {
+  SmallAttribute() : super('small', AttributeScope.INLINE, true);
+}
+
 class UnderlineAttribute extends Attribute<bool> {
   UnderlineAttribute() : super('underline', AttributeScope.INLINE, true);
 }

lib/src/widgets/default_styles.dart

@@ -51,6 +51,7 @@ class DefaultStyles {
     this.paragraph,
     this.bold,
     this.italic,
+    this.small,
     this.underline,
     this.strikeThrough,
     this.link,
@@ -73,6 +74,7 @@ class DefaultStyles {
   final DefaultTextBlockStyle? paragraph;
   final TextStyle? bold;
   final TextStyle? italic;
+  final TextStyle? small;
   final TextStyle? underline;
   final TextStyle? strikeThrough;
   final TextStyle? sizeSmall; // 'small'
@@ -147,6 +149,7 @@ class DefaultStyles {
             baseStyle, const Tuple2(0, 0), const Tuple2(0, 0), null),
         bold: const TextStyle(fontWeight: FontWeight.bold),
         italic: const TextStyle(fontStyle: FontStyle.italic),
+        small: const TextStyle(fontSize: 12),
         underline: const TextStyle(decoration: TextDecoration.underline),
         strikeThrough: const TextStyle(decoration: TextDecoration.lineThrough),
         link: TextStyle(
@@ -205,6 +208,7 @@ class DefaultStyles {
         paragraph: other.paragraph ?? paragraph,
         bold: other.bold ?? bold,
         italic: other.italic ?? italic,
+        small: other.small ?? small,
         underline: other.underline ?? underline,
         strikeThrough: other.strikeThrough ?? strikeThrough,
         link: other.link ?? link,

lib/src/widgets/text_line.dart

@@ -181,6 +181,7 @@ class TextLine extends StatelessWidget {
     <String, TextStyle?>{
       Attribute.bold.key: defaultStyles.bold,
       Attribute.italic.key: defaultStyles.italic,
+      Attribute.small.key: defaultStyles.small,
       Attribute.link.key: defaultStyles.link,
       Attribute.underline.key: defaultStyles.underline,
       Attribute.strikeThrough.key: defaultStyles.strikeThrough,

lib/src/widgets/toolbar.dart

@@ -65,6 +65,7 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
     double toolbarIconSize = kDefaultIconSize,
     bool showBoldButton = true,
     bool showItalicButton = true,
+    bool showSmallButton = false,
     bool showUnderLineButton = true,
     bool showStrikeThrough = true,
     bool showColorButton = true,
@@ -96,6 +97,7 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
       showHistory ||
           showBoldButton ||
           showItalicButton ||
+          showSmallButton ||
           showUnderLineButton ||
           showStrikeThrough ||
           showColorButton ||
@@ -142,6 +144,13 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
             iconSize: toolbarIconSize,
             controller: controller,
           ),
+        if (showSmallButton)
+          ToggleStyleButton(
+            attribute: Attribute.small,
+            icon: Icons.format_size,
+            iconSize: toolbarIconSize,
+            controller: controller,
+          ),
         if (showUnderLineButton)
           ToggleStyleButton(
             attribute: Attribute.underline,