clarify Data Block in the Frame format documentation

as requested in #1156

doc/lz4_Frame_format.md

@@ -16,7 +16,7 @@ Distribution of this document is unlimited.
 
 ### Version
 
-1.6.2 (12/08/2020)
+1.6.3 (12/09/2022)
 
 
 Introduction
@@ -61,9 +61,9 @@ and associated error message explaining which parameter is unsupported.
 General Structure of LZ4 Frame format
 -------------------------------------
 
-| MagicNb | F. Descriptor | Block | (...) | EndMark | C. Checksum |
-|:-------:|:-------------:| ----- | ----- | ------- | ----------- |
-| 4 bytes |  3-15 bytes   |       |       | 4 bytes | 0-4 bytes   |
+| MagicNb | F. Descriptor | Data Block | (...) | EndMark | C. Checksum |
+|:-------:|:-------------:| ---------- | ----- | ------- | ----------- |
+| 4 bytes |  3-15 bytes   |            |       | 4 bytes | 0-4 bytes   |
 
 __Magic Number__
 
@@ -269,7 +269,7 @@ The size does not include the block checksum if present.
 
 _Block_Size_ shall never be larger than _Block_Maximum_Size_.
 Such an outcome could potentially happen for non-compressible sources.
-In such a case, such data block must be passed using uncompressed format.
+In such a case, such data block **must** be passed using uncompressed format.
 
 A value of `0x00000000` is invalid, and signifies an _EndMark_ instead.
 Note that this is different from a value of `0x80000000` (highest bit set),
@@ -397,6 +397,8 @@ and trigger an error if it does not fit within acceptable range.
 Version changes
 ---------------
 
+1.6.3 : minor : clarify Data Block
+
 1.6.2 : clarifies specification of _EndMark_
 
 1.6.1 : introduced terms "LZ4 Frame Header" and "LZ4 Frame Footer"