Add docs from gofiber/fiber@6d1f7b2

Author: github-actions[bot]

docs/core/middleware/compress.md

@@ -10,6 +10,12 @@ Compression middleware for [Fiber](https://github.com/gofiber/fiber) that automa
 Bodies smaller than 200 bytes remain uncompressed because compression would likely increase their size and waste CPU cycles. [See the fasthttp source](https://github.com/valyala/fasthttp/blob/497922a21ef4b314f393887e9c6147b8c3e3eda4/http.go#L1713-L1715).
 :::
 
+## Behavior
+
+- Skips compression for responses that already define `Content-Encoding`, for range requests, `206` responses, status codes without bodies, or when either side sends `Cache-Control: no-transform`.
+- `HEAD` requests negotiate compression so `Content-Encoding`, `Content-Length`, `ETag`, and `Vary` reflect the encoded representation, but the body is removed before sending.
+- When compression runs, strong `ETag` values are recomputed from the compressed bytes; when skipped, `Accept-Encoding` is still merged into `Vary` unless the header is `*` or already present.
+
 ## Signatures
 
 ```go

docs/core/whats_new.md

@@ -1182,7 +1182,11 @@ We've updated several fields from a single string (containing comma-separated va
 
 ### Compression
 
-We've added support for `zstd` compression on top of `gzip`, `deflate`, and `brotli`.
+- Added support for `zstd` compression alongside `gzip`, `deflate`, and `brotli`.
+- Strong `ETag` values are now recomputed for compressed payloads so validators remain accurate.
+- Compression is bypassed for responses that already specify `Content-Encoding`, for range requests or `206` statuses, and when either side sends `Cache-Control: no-transform`.
+- `HEAD` requests still negotiate compression so `Content-Encoding`, `Content-Length`, `ETag`, and `Vary` match a corresponding `GET`, but the body is omitted.
+- `Vary: Accept-Encoding` is merged into responses even when compression is skipped, preventing caches from mixing encoded and unencoded variants.
 
 ### CSRF