diff --git a/objectivec/GPBExtensionRegistry.h b/objectivec/GPBExtensionRegistry.h
index 0363c70..d79632d 100644
--- a/objectivec/GPBExtensionRegistry.h
+++ b/objectivec/GPBExtensionRegistry.h
@@ -35,30 +35,50 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
-// A table of known extensions, searchable by name or field number.  When
-// parsing a protocol message that might have extensions, you must provide an
-// ExtensionRegistry in which you have registered any extensions that you want
-// to be able to parse.  Otherwise, those extensions will just be treated like
-// unknown fields.
-//
-// The *Root classes provide +extensionRegistry for the extensions defined in a
-// given file *and* all files it imports.  You can also create a
-// GPBExtensionRegistry, and merge those registries to handle parsing extensions
-// defined from non overlapping files.
-//
-//    GPBExtensionRegistry *registry =
-//        [[[MyProtoFileRoot extensionRegistry] copy] autorelease];
-//    [registry addExtension:[OtherMessage neededExtension];  // Not in MyProtoFile
-//    NSError *parseError = nil;
-//    MyMessage *msg = [MyMessage parseData:data
-//                        extensionRegistry:registry
-//                                    error:&parseError];
-//
+/**
+ * A table of known extensions, searchable by name or field number.  When
+ * parsing a protocol message that might have extensions, you must provide a
+ * GPBExtensionRegistry in which you have registered any extensions that you
+ * want to be able to parse. Otherwise, those extensions will just be treated
+ * like unknown fields.
+ *
+ * The *Root classes provide `+extensionRegistry` for the extensions defined
+ * in a given file *and* all files it imports. You can also create a
+ * GPBExtensionRegistry, and merge those registries to handle parsing
+ * extensions defined from non overlapping files.
+ *
+ * ```
+ * GPBExtensionRegistry *registry = [[MyProtoFileRoot extensionRegistry] copy];
+ * [registry addExtension:[OtherMessage neededExtension]]; // Not in MyProtoFile
+ * NSError *parseError;
+ * MyMessage *msg = [MyMessage parseData:data extensionRegistry:registry error:&parseError];
+ * ```
+ **/
 @interface GPBExtensionRegistry : NSObject<NSCopying>
 
+/**
+ * Adds the given GPBExtensionDescriptor to this registry.
+ *
+ * @param extension The extension description to add.
+ **/
 - (void)addExtension:(GPBExtensionDescriptor *)extension;
+
+/**
+ * Adds all the extensions from another registry to this registry.
+ *
+ * @param registry The registry to merge into this registry.
+ **/
 - (void)addExtensions:(GPBExtensionRegistry *)registry;
 
+/**
+ * Looks for the extension registered for the given field number on a given
+ * GPBDescriptor.
+ *
+ * @param descriptor  The descriptor to look for a registered extension on.
+ * @param fieldNumber The field number of the extension to look for.
+ *
+ * @return The registered GPBExtensionDescriptor or nil if none was found.
+ **/
 - (nullable GPBExtensionDescriptor *)extensionForDescriptor:(GPBDescriptor *)descriptor
                                                 fieldNumber:(NSInteger)fieldNumber;