diff --git a/graphics/common/aidl/android/hardware/graphics/common/StandardMetadataType.aidl b/graphics/common/aidl/android/hardware/graphics/common/StandardMetadataType.aidl
index 68c99ee..43cf672 100644
--- a/graphics/common/aidl/android/hardware/graphics/common/StandardMetadataType.aidl
+++ b/graphics/common/aidl/android/hardware/graphics/common/StandardMetadataType.aidl
@@ -24,6 +24,15 @@
  *
  * IMapper@4.x must support getting the following standard buffer metadata types. IMapper@4.x may
  * support setting these standard buffer metadata types as well.
+ *
+ * When encoding these StandardMetadataTypes into a byte stream, the associated MetadataType is
+ * is first encoded followed by the StandardMetadataType value. The MetadataType is encoded by
+ * writing the length of MetadataType.name using 8 bytes in little endian, followed by a char
+ * array of MetadataType.name's characters. The char array is not null terminated. Finally,
+ * MetadataType.value is represented by 8 bytes written in little endian.
+ *
+ * The StandardMetadataType encode/decode support library can be found in:
+ * frameworks/native/libs/gralloc/types/include/gralloctypes/Gralloc4.h.
  */
 @VintfStability
 @Backing(type="long")
diff --git a/graphics/mapper/4.0/IMapper.hal b/graphics/mapper/4.0/IMapper.hal
index 3be2152..93c85bd 100644
--- a/graphics/mapper/4.0/IMapper.hal
+++ b/graphics/mapper/4.0/IMapper.hal
@@ -206,6 +206,9 @@
      * outside of @p accessRegion is undefined, except that it must not cause
      * process termination.
      *
+     * An accessRegion of all-zeros means the entire buffer. That is, it is
+     * equivalent to '(0,0)-(buffer width, buffer height)'.
+     *
      * This function can lock both single-planar and multi-planar formats. The caller
      * should use get() to get information about the buffer they are locking.
      * get() can be used to get information about the planes, offsets, stride,