From a65ee073906545a75307f82bffec5f48c514e3f6 Mon Sep 17 00:00:00 2001
From: Anders Hartvoll Ruud <andruud@google.com>
Date: Wed, 28 May 2025 08:45:54 +0000
Subject: [PATCH] [css-mixins-1] Check default values against the parameter
 type

---
 css-mixins-1/Overview.bs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/css-mixins-1/Overview.bs b/css-mixins-1/Overview.bs
index e7fb8256b4d..3a828f2295a 100644
--- a/css-mixins-1/Overview.bs
+++ b/css-mixins-1/Overview.bs
@@ -201,11 +201,17 @@ and optionally a <dfn>default value</dfn>.
 	<<declaration-rule-list>>
 }
 
-<dfn><<function-parameter>></dfn> = <<custom-property-name>> <<css-type>>? [ : <<declaration-value>> ]?
+<dfn><<function-parameter>></dfn> = <<custom-property-name>> <<css-type>>? [ : <<default-value>> ]?
 <dfn><<css-type>></dfn> = <<syntax-component>> | <<type()>>
+<dfn><<default-value>></dfn> = <<declaration-value>>
 <dfn function lt="type()" for="@function">&lt;type()></dfn> = type( <<syntax>> )
 </pre>
 
+If a [=default value=] and a [=parameter type=] are both provided,
+then the [=default value=] must [=CSS/parse=] successfully
+according to that [=parameter type=]'s syntax.
+Otherwise, the ''@function'' rule is invalid.
+
 <h4 id=function-preamble>
 The Function Preamble</h4>