webp-container-spec.txt: clarify 'VP8 '/'XMP ' fourccs
Note the fourth character is an ASCII space to avoid confusion.
Also update the FourCC definition to mention that they're case
sensitive.
@@ -84,7 +84,8 @@ _uint32_
_FourCC_
: A _FourCC_ (four-character code) is a _uint32_ created by concatenating four
- ASCII characters in little-endian order.
+ ASCII characters in little-endian order. This means 'aaaa' (%x61.61.61.61) and
+ 'AAAA' (%x41.41.41.41) are treated as different _FourCCs_.
_1-based_
@@ -203,6 +204,8 @@ VP8 data: _Chunk Size_ bytes
: VP8 bitstream data.
+Note the fourth character in the 'VP8 ' fourcc is an ASCII space (%x20).
+
The VP8 bitstream format specification can be found at [VP8 Data Format and
Decoding Guide][vp8spec]. Note that the VP8 frame header contains the VP8 frame
width and height. That is assumed to be the width and height of the canvas.
@@ -714,6 +717,8 @@ XMP Metadata: _Chunk Size_ bytes
: image metadata in XMP format.
+Note the fourth character in the 'XMP ' fourcc is an ASCII space (%x20).
+
Additional guidance about handling metadata can be found in the
Metadata Working Group's [Guidelines for Handling Metadata][metadata].
