Resolve to the default value when the type is wrong.

css-mixins-1/Overview.bs

@@ -226,27 +226,21 @@ described in [[!css-variables]].
 			the |dashed function|'s name as a [=tree-scoped reference=].
 			If no such name exists, return failure.
 		2. Let |dependency values| be an initially empty [=list=].
-		2. For each |dependency| in |function|'s [=function dependency|dependencies=]:
+		3. For each |dependency| in |function|'s [=function dependency|dependencies=]:
 			* Let |dependency value| be the value that would be substituted
 				if a ''var()'' function had been specified explicitly
 				at the end of |dashed function|'s argument list,
 				with |dependency| as its only argument.
 			* If that substitution would have made a containing declaration
 				[=invalid at computed-value time=],
 				set |dependency value| to the [=guaranteed-invalid value=].
-			* If |dependency value| is the [=guaranteed-invalid value=],
-				and |dependency| has a [=default value=],
-				set |dependency value| to that [=default value=].
-			* If |dependency| has a [=parameter type|type=],
-				set |dependency value| to the result of
-				[=resolve a typed value|resolving a typed value=],
-				using |dependency value| as the value,
-				and the [=syntax definition=] associated with the dependency's type as the syntax.
-			* Append |dependency value| to |dependency values|.
-		1. [=Evaluate a custom function=],
+			* Append the result of [=resolving an argument=] to |dependency values|,
+				using |dependency value| as value,
+				and |dependency| as parameter.
+		4. [=Evaluate a custom function=],
 			using |function|, |dashed function| and |dependency values|.
-		2. If failure was returned, return failure.
-		3. Otherwise,
+		5. If failure was returned, return failure.
+		6. Otherwise,
 			replace the <<dashed-function>> with the [=equivalent token sequence=]
 			of the value resulting from the evaluation.
 </div>
@@ -273,28 +267,50 @@ Evaluating Custom Functions {#evaluating-custom-functions}
 		at the same index:
 		* If |argument| does not exist,
 			set |argument| to the [=guaranteed-invalid value=].
-		* If |argument| is the [=guaranteed-invalid value=],
-			and |parameter| has a [=default value=],
-			set |argument| to that [=default value=].
-		* If |parameter| has a [=parameter type|type=],
-			set |argument| to the result of
-			[=resolve a typed value|resolving a typed value=],
-			using |argument| as the |value|,
-			and the [=syntax definition=] associated with the parameter's type as the |syntax|.
-		* Replace the value in |dashed function|'s argument list with |argument|.
+		* Replace the value in |dashed function|'s argument list
+			with the result of [=resolving an argument=],
+			using |argument| as value,
+			and |parameter| as parameter.
 	3. Let |result| be the [=resolved local value=]
 		of the '@function/result' descriptor,
 		using |function|, |dashed function|, and |dependency values|.
 	4. If |function| has a [=return type=],
 		set |result| to the result of [=resolve a typed value|resolving a typed value=],
-		using |result| as the |value|,
-		and the [=syntax definition=] associated with the [=return type=] as the |syntax|.
+		using |result| as the value,
+		and the [=syntax definition=] associated with the [=return type=] as the syntax.
 	5. If |result| is the [=guaranteed-invalid value=],
 		return failure.
 	6. Otherwise,
 		return |result|.
 </div>
 
+<div algorithm>
+	To <dfn>resolve an argument</dfn>,
+	with value |value|,
+	and [=function parameter|parameter=] |parameter|:
+
+	1. If |value| is not the [=guaranteed-invalid value=],
+		and |parameter| has a [=parameter type|type=],
+		set |value| to the result of [=resolve a typed value|resolving a typed value=]
+		using |value| as the value,
+		and the [=syntax definition=] associated with |parameter|'s type as the syntax.
+		<span class=note>This step may cause |value| to become [=guaranteed-invalid value|guaranteed-invalid=].</span>
+	2. If |value| is the [=guaranteed-invalid value=],
+		and |parameter| has a [=default value=],
+		set |value| to one of the following:
+		<dl class="switch">
+			:   If |parameter| has a [=parameter type|type=]
+			::  The result of [=resolve a typed value|resolving a typed value=]
+				using the |parameter|'s [=default value=] as the value,
+				and the [=syntax definition=] associated with |parameter|'s type as the syntax.
+
+			:   Otherwise
+			::  The |parameter|'s [=default value=].
+		</dl>
+	3. Return |value|.
+
+</div>
+
 <div algorithm>
 	To <dfn>resolve a typed value</dfn>,
 	with value |value|,