diff --git a/sc2/doc/devel/gfxres b/sc2/doc/devel/gfxres
index bdf7127a1..79abb09be 100644
--- a/sc2/doc/devel/gfxres
+++ b/sc2/doc/devel/gfxres
@@ -4,8 +4,11 @@ This is the format for resources of type GFXRES (these have the extension
 Everything is stored MSB first unless otherwise specified.
 
 position   length  meaning
-           4       Unknown, always 0xffffffff
-           4       Unknown, always 0x00000000
+           4       0xffffffff if the file is uncompressed.
+                   Otherwise, the file is compressed. When uncompressed, the
+                   file complies with the rest of the format as described
+                   below.
+           4       Unused in file, always 0x00000000
            4       FlagsAndIndex:
                      bits 0-11: 1 less than the number of frames in this
                                 graphics resource
diff --git a/sc2/doc/devel/strtab b/sc2/doc/devel/strtab
index 7341cfa77..a23c1f7b2 100644
--- a/sc2/doc/devel/strtab
+++ b/sc2/doc/devel/strtab
@@ -6,8 +6,11 @@ and colour translation tables (.xlt).
 Everything is stored MSB first unless otherwise specified.
 
 position   length  meaning
-           4       Unknown, always 0xffffffff
-           2       Unknown, always 0x0000
+           4       0xffffffff if the file is uncompressed.
+                   Otherwise, the file is compressed. When uncompressed, the
+                   file complies with the rest of the format as described
+                   below.
+           2       Unused in file, always 0x0000
            2       number of items in the file (StringCount)
 
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