diff --git a/objectivec/GPBUnknownField.h b/objectivec/GPBUnknownField.h
index 12d72a9..5b96023 100644
--- a/objectivec/GPBUnknownField.h
+++ b/objectivec/GPBUnknownField.h
@@ -36,23 +36,62 @@
 @class GPBUnknownFieldSet;
 
 NS_ASSUME_NONNULL_BEGIN
-
+/**
+ * Store an unknown field. These are used in conjunction with
+ * GPBUnknownFieldSet.
+ **/
 @interface GPBUnknownField : NSObject<NSCopying>
 
+/** Initialize a field with the given number. */
+- (instancetype)initWithNumber:(int32_t)number;
+
+/** The field number the data is stored under. */
 @property(nonatomic, readonly, assign) int32_t number;
 
-// Only one of these will be set.
+/** An array of varint values for this field. */
 @property(nonatomic, readonly, strong) GPBUInt64Array *varintList;
-@property(nonatomic, readonly, strong) GPBUInt32Array *fixed32List;
-@property(nonatomic, readonly, strong) GPBUInt64Array *fixed64List;
-@property(nonatomic, readonly, strong) NSArray *lengthDelimitedList;  // NSData
-@property(nonatomic, readonly, strong) NSArray *groupList;  // GPBUnknownFieldSet
 
-// Only one of these should be used per Field.
+/** An array of fixed32 values for this field. */
+@property(nonatomic, readonly, strong) GPBUInt32Array *fixed32List;
+
+/** An array of fixed64 values for this field. */
+@property(nonatomic, readonly, strong) GPBUInt64Array *fixed64List;
+
+/** An array of data values for this field. */
+@property(nonatomic, readonly, strong) NSArray<NSData*> *lengthDelimitedList;
+
+/** An array of groups of values for this field. */
+@property(nonatomic, readonly, strong) NSArray<GPBUnknownFieldSet*> *groupList;
+
+/**
+ * Add a value to the varintList.
+ *
+ * @param value The value to add.
+ **/
 - (void)addVarint:(uint64_t)value;
+/**
+ * Add a value to the fixed32List.
+ *
+ * @param value The value to add.
+ **/
 - (void)addFixed32:(uint32_t)value;
+/**
+ * Add a value to the fixed64List.
+ *
+ * @param value The value to add.
+ **/
 - (void)addFixed64:(uint64_t)value;
+/**
+ * Add a value to the lengthDelimitedList.
+ *
+ * @param value The value to add.
+ **/
 - (void)addLengthDelimited:(NSData *)value;
+/**
+ * Add a value to the groupList.
+ *
+ * @param value The value to add.
+ **/
 - (void)addGroup:(GPBUnknownFieldSet *)value;
 
 @end