diff --git a/starboard/drm.h b/starboard/drm.h
index 1fcebb06f0c9..ebf7c64dd1f0 100644
--- a/starboard/drm.h
+++ b/starboard/drm.h
@@ -48,13 +48,13 @@ typedef enum SbDrmStatus {
   kSbDrmStatusNotSupportedError,
   kSbDrmStatusInvalidStateError,
   kSbDrmStatusQuotaExceededError,
-  // The following error can be used when the error status cannot be mapped to
-  // one of the above errors.
+  // The kSbDrmStatusUnknownError can be used when the error status cannot be
+  // mapped to one of the rest errors.
   kSbDrmStatusUnknownError,
 } SbDrmStatus;
 
 // Status of a particular media key.
-// https://w3c.github.io/encrypted-media/#idl-def-MediaKeyStatus
+// https://www.w3.org/TR/encrypted-media/#idl-def-mediakeystatus
 typedef enum SbDrmKeyStatus {
   kSbDrmKeyStatusUsable,
   kSbDrmKeyStatusExpired,
@@ -180,8 +180,14 @@ typedef void (*SbDrmSessionUpdatedFunc)(SbDrmSystem drm_system,
                                         int session_id_size);
 
 // A callback for notifications that the status of one or more keys in a session
-// has been changed.  All keys of the session and their new status will be
-// passed along.  Any keys not in the list is considered as deleted.
+// has been changed.  All keys |key_ids| of the session and their new status
+// will be passed along.  Any keys not in the list are considered as deleted.
+//
+// |number_of_keys| is the number of keys.
+//
+// |key_ids| is a pointer of a vector contains keys.
+//
+// |key_statuses| is a pointer of a vector contains the status of each key.
 typedef void (*SbDrmSessionKeyStatusesChangedFunc)(
     SbDrmSystem drm_system,
     void* context,
@@ -191,7 +197,7 @@ typedef void (*SbDrmSessionKeyStatusesChangedFunc)(
     const SbDrmKeyId* key_ids,
     const SbDrmKeyStatus* key_statuses);
 
-// A callback for signalling that a session has been closed by the SbDrmSystem
+// A callback for signalling that a session has been closed by the SbDrmSystem.
 typedef void (*SbDrmSessionClosedFunc)(SbDrmSystem drm_system,
                                        void* context,
                                        const void* session_id,
@@ -294,9 +300,11 @@ SB_EXPORT SbDrmSystem SbDrmCreateSystem(
 // used.
 //
 // |type|: The case-sensitive type of the session update request payload. Must
-//   not be NULL.
+// not be NULL.
+//
 // |initialization_data|: The data for which the session update
-//   request payload is created. Must not be NULL.
+// request payload is created. Must not be NULL.
+//
 // |initialization_data_size|: The size of the session update request payload.
 SB_EXPORT void SbDrmGenerateSessionUpdateRequest(
     SbDrmSystem drm_system,
@@ -353,14 +361,17 @@ SB_EXPORT bool SbDrmIsServerCertificateUpdatable(SbDrmSystem drm_system);
 // |SbDrmIsServerCertificateUpdatable| is called first and returned true.
 //
 // |drm_system|: The DRM system whose server certificate is being updated. Must
-//   not be |kSbDrmSystemInvalid|.
+// not be |kSbDrmSystemInvalid|.
+//
 // |ticket|: The opaque ID that allows to distinguish callbacks from multiple
-//   concurrent calls to SbDrmUpdateServerCertificate(), which will be passed to
-//   |server_certificate_updated_callback| as-is. It is the responsibility of
-//   the caller to establish ticket uniqueness, issuing multiple requests with
-//   the same ticket may result in undefined behavior. The value
-//   |kSbDrmTicketInvalid| must not be used.
+// concurrent calls to SbDrmUpdateServerCertificate(), which will be passed to
+// |server_certificate_updated_callback| as-is. It is the responsibility of
+// the caller to establish ticket uniqueness, issuing multiple requests with
+// the same ticket may result in undefined behavior. The value
+// |kSbDrmTicketInvalid| must not be used.
+//
 // |certificate|: Pointer to the server certificate data. Must not be NULL.
+//
 // |certificate_size|: Size of the server certificate data.
 SB_EXPORT void SbDrmUpdateServerCertificate(SbDrmSystem drm_system,
                                             int ticket,