diff --git a/CHANGELOG.md b/CHANGELOG.md
index 34ef832..1fcb5f8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,9 @@
 ## 1.1.0
 
 * Make the constructor for ExtensionSet public, for tools like dartdoc.
+* Split the `gitHub` ExtensionSet into two sets: `gitHubFlavored`, which
+  represents the GitHub Flavored Markdown spec, and `gitHubWeb`, which
+  represents what GitHub actually renders Markdown.
 
 ## 1.0.0
 
diff --git a/README.md b/README.md
index 9970e28..dcaca0d 100644
--- a/README.md
+++ b/README.md
@@ -69,9 +69,13 @@
   * `new InlineHtmlSyntax()`
   * `const FencedCodeBlockSyntax()`
 
-* `ExtensionSet.gitHub` includes five extensions:
+* `ExtensionSet.gitHubWeb` includes five extensions:
 
   * `new InlineHtmlSyntax()`
+  * `const HeaderWithIdSyntax()`, which adds `id` attributes to ATX-style
+    headers, for easy intra-document linking.
+  * `const SetextHeaderWithIdSyntax()`, which adds `id` attributes to
+    Setext-style headers, for easy intra-document linking.
   * `const FencedCodeBlockSyntax()`
   * `const TableSyntax()`
 
diff --git a/example/app.dart b/example/app.dart
index e0f4c53..9f7c164 100644
--- a/example/app.dart
+++ b/example/app.dart
@@ -25,7 +25,7 @@
 final extensionSets = {
   'basic-radio': md.ExtensionSet.none,
   'commonmark-radio': md.ExtensionSet.commonMark,
-  'gfm-radio': md.ExtensionSet.gitHub,
+  'gfm-radio': md.ExtensionSet.gitHubWeb,
 };
 
 void main() {
diff --git a/lib/src/extension_set.dart b/lib/src/extension_set.dart
index 863004f..d18337a 100644
--- a/lib/src/extension_set.dart
+++ b/lib/src/extension_set.dart
@@ -7,15 +7,51 @@
 /// For example, the [gitHub] set of syntax extensions allows users to output
 /// HTML from their Markdown in a similar fashion to GitHub's parsing.
 class ExtensionSet {
+  /// The [none] extension set renders Markdown similar to [Markdown.pl].
+  ///
+  /// However, this set does not render _exactly_ the same as Markdown.pl;
+  /// rather it is more-or-less the CommonMark standard of Markdown, without
+  /// fenced code blocks, or inline HTML.
+  ///
+  /// [Markdown.pl]: http://daringfireball.net/projects/markdown/syntax
   static final ExtensionSet none = new ExtensionSet([], []);
 
+  /// The [commonMark] extension set is close to compliance with [CommonMark].
+  ///
+  /// [CommonMark]: http://commonmark.org/
   static final ExtensionSet commonMark = new ExtensionSet(
       [const FencedCodeBlockSyntax()], [new InlineHtmlSyntax()]);
 
-  static final ExtensionSet gitHub = new ExtensionSet(
+  /// The [gitHubWeb] extension set renders Markdown similarly to GitHub.
+  ///
+  /// This is different from the [gitHubFlavored] extension set in that GitHub
+  /// actually renders HTML different from straight [GitHub flavored Markdown].
+  ///
+  /// (The only difference currently is that [gitHubWeb] renders headers with
+  /// linkable IDs.)
+  ///
+  /// [GitHub flavored Markdown]: https://github.github.com/gfm/
+  static final ExtensionSet gitHubWeb = new ExtensionSet([
+    const FencedCodeBlockSyntax(),
+    const HeaderWithIdSyntax(),
+    const SetextHeaderWithIdSyntax(),
+    const TableSyntax()
+  ], [
+    new InlineHtmlSyntax()
+  ]);
+
+  /// The [gitHubFlavored] extension set is close to compliance with the [GitHub
+  /// flavored Markdown spec].
+  ///
+  /// [GitHub flavored Markdown]: https://github.github.com/gfm/
+  static final ExtensionSet gitHubFlavored = new ExtensionSet(
       [const FencedCodeBlockSyntax(), const TableSyntax()],
       [new InlineHtmlSyntax()]);
 
+  /// The deprecated name for the [gitHubFlavored] extension set.
+  @deprecated
+  static final ExtensionSet gitHub = gitHubFlavored;
+
   final List<BlockSyntax> blockSyntaxes;
   final List<InlineSyntax> inlineSyntaxes;
 
diff --git a/tool/stats_lib.dart b/tool/stats_lib.dart
index 8d06e79..15290aa 100644
--- a/tool/stats_lib.dart
+++ b/tool/stats_lib.dart
@@ -45,7 +45,7 @@
   static final Config commonMarkConfig =
       new Config._('common_mark', 'http://spec.commonmark.org/0.28/', null);
   static final Config gfmConfig = new Config._(
-      'gfm', 'https://github.github.com/gfm/', ExtensionSet.gitHub);
+      'gfm', 'https://github.github.com/gfm/', ExtensionSet.gitHubFlavored);
 
   final String prefix;
   final String baseUrl;