diff --git a/src/pip/_internal/req/req_file.py b/src/pip/_internal/req/req_file.py
index f6ba70fe7f6..376e465f457 100644
--- a/src/pip/_internal/req/req_file.py
+++ b/src/pip/_internal/req/req_file.py
@@ -595,6 +595,11 @@ def get_file_content(url: str, session: "PipSession") -> Tuple[str, str]:
 
 
 def _decode_req_file(data: bytes, url: str) -> str:
+    # NOTE: Byte Order Marks other than the UTF-8 BOM (used by PEP 263)
+    # aren't allowed as per the requirements.txt spec, but deprecating
+    # them isn't feasible as Windows Powershell uses UTF-16 (usually
+    # encountered while redirecting output to a requirements.txt).
+    # Thus, they remain as implementation-defined behaviour :/
     for bom, encoding in BOMS:
         if data.startswith(bom):
             return data[len(bom) :].decode(encoding)