URL-SYNTAX: mention how FILE:// access can access network on windows

Closes #6314

diff --git a/docs/URL-SYNTAX.md b/docs/URL-SYNTAX.md
index 7892aa611d72e209258189f580246576e8a141ed..f724f75f861614efe8035bd5ab35ad997dfe2ce3 100644 (file)
--- a/docs/URL-SYNTAX.md
+++ b/docs/URL-SYNTAX.md
@@ -200,9 +200,16 @@ curl only allows the hostname part of a FILE URL to be one out of these three
 alternatives: `localhost`, `127.0.0.1` or blank ("", zero characters).
 Anything else will make curl fail to parse the URL.
 
-On Windows, curl accepts that the FILE URL's path starts with a "drive
-letter". That's a single letter `a` to `z` followed by a colon or a pipe
-character (`|`).
+### Windows-specific FILE details
+
+curl accepts that the FILE URL's path starts with a "drive letter". That's a
+single letter `a` to `z` followed by a colon or a pipe character (`|`).
+
+The Windows operating system itself will convert some file accesses to perform
+network accesses over SMB/CIFS, through several different file path patterns.
+This way, a `file://` URL passed to curl *might* be converted into a network
+access inadvertently and unknowingly to curl. This is a Windows feature curl
+cannot control or disable.
 
 ## IMAP