updated frame specification with recommended max window size

diff --git a/zstd_frame_format.md b/zstd_frame_format.md
index d27b2c76d392fecf1c6c8635f0ca4137a46c1a3b..61b5aef58ea6ede54cadb135286bb2e0021d8631 100644 (file)
--- a/zstd_frame_format.md
+++ b/zstd_frame_format.md
@@ -194,11 +194,11 @@ __WD byte__ (Window Descriptor)
 
 Provides guarantees on maximum back-reference distance
 that will be used within compressed data.
-This information can then be used by decoder to allocate enough memory.
+This information is useful for decoders to allocate enough memory.
 
-|  BitNb  |    7-3   |    0-2   |
-| ------- | -------- | -------- |
-|FieldName| Exponent | Mantissa |
+|   BitNb   |    7-3   |    0-2   |
+| --------- | -------- | -------- |
+| FieldName | Exponent | Mantissa |
 
 Maximum distance is given by the following formulae :
 ```
@@ -207,12 +207,18 @@ windowBase = 1 << windowLog;
 windowAdd = (windowBase / 8) * Mantissa;
 windowSize = windowBase + windowAdd;
 ```
+The minimum window size is 1 KB.
+The maximum value is (15*(2^38))-1 bytes, which is almost 1.875 TB.
+
 `WD` byte is optional. It's not present in `single segment` mode.
+In which case, the maximum back-reference distance is the content size itself, which can be any value from 1 to 2^64-1 bytes (16 EB).
 
-In order to preserve decoder from unreasonable memory requirement,
+In order to preserve decoder from unreasonable memory requirements,
 a decoder can refuse a compressed frame
 which requests a memory size beyond decoder's authorized range.
 
+For better interoperability, decoders are recommended to be compatible with window sizes up to 8 MB. Encoders are recommended to not request more than 8 MB. It's just a recommendation, decoders are free to accept or refuse larger or lower values.
+
 __Frame Content Size__
 
 This is the original (uncompressed) size.