[master] b49013193 answer an XXX comment question

[Nils Goroll]

commit b4901319364a70afb5990d288218f90f701a5c05
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Fri Feb 14 12:05:16 2025 +0100

    answer an XXX comment question
    
    Basically copied from a -commit email

diff --git a/bin/varnishd/cache/cache_vrt_filter.c b/bin/varnishd/cache/cache_vrt_filter.c
index 43ef51362..2ebe3183d 100644
--- a/bin/varnishd/cache/cache_vrt_filter.c
+++ b/bin/varnishd/cache/cache_vrt_filter.c
@@ -450,7 +450,13 @@ req_Empty_Filter(struct req *req)
 }
 
 /*--------------------------------------------------------------------
- * XXX: why ignore needless filters for everything but req?
+ * control if "set req.filters" is allowed
+ *
+ * req.body (conversely to other body object) is one where VCL has control over
+ * when it gets processed by means of std.cache_req_body(): Filters act on the
+ * received body when that function is called, so confusion could be caused if
+ * people expect filters to have an effect when set/changed after the req.body
+ * is already cached.
  */
 
 static int