From e627f547cfca8a8a4f9e2bad445d66ceec18a18d Mon Sep 17 00:00:00 2001
From: Will Dietz <will.dietz@sifive.com>
Date: Mon, 6 Mar 2023 11:30:30 -0600
Subject: [PATCH] spec: fix forwarding-references-upwards header org, add
 downwards blurb.

---
 spec.md | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/spec.md b/spec.md
index 4461d712..46f6ca77 100644
--- a/spec.md
+++ b/spec.md
@@ -1919,7 +1919,7 @@ module RefProducer :
     define thereg = probe(myreg)
 ```
 
-### Forwarding References Upwards
+#### Forwarding References Upwards
 
 Define statements can be used to forward a child module's reference further up
 the hierarchy:
@@ -1951,6 +1951,26 @@ module Forward :
   define p = f.p[0][1]
 ```
 
+#### Forwarding References Downwards
+
+Define statements can also be used to forward references down the hierarchy
+using input reference-type ports, which are allowed but should be used
+carefully as they make it possible to express
+invalid reference paths.
+
+See [@sec:input-references] for more details, a small example is given below:
+
+```firrtl
+module UnusedInputRef :
+  input r : Probe<UInt<1>>
+
+module ForwardDownwards :
+  input in : UInt<1>
+
+  inst u of UnusedInputRef
+  define u.r = probe(in)
+```
+
 ### Force and Release
 
 To override existing drivers for a `RWProbe`{.firrtl}, the `force`{.firrtl}