[css-variables-1] Custom props that are IACVT become guaranteed-invalid (w3c#6006)

Co-authored-by: Anders Hartvoll Ruud <andruud@google.com>

Author: andruud

css-variables-1/Overview.bs

@@ -308,8 +308,7 @@ Resolving Dependency Cycles</h3>
 
 	If there is a cycle in the dependency graph,
 	all the <a>custom properties</a> in the cycle
-	are <dfn export>cyclic at computed-value time</dfn>,
-	and must compute to the [=guaranteed-invalid value=].
+	are [=invalid at computed-value time=].
 
 	Note: Defined properties that participate in a dependency cycle
 	either end up with invalid variables in their value
@@ -345,7 +344,7 @@ Resolving Dependency Cycles</h3>
 		}
 		</pre>
 
-		Both '--one' and '--two' are now [=cyclic at computed-value time=],
+		Both '--one' and '--two' are now [=invalid at computed-value time=],
 		and compute to the [=guaranteed-invalid value=]
 		rather than lengths.
 	</div>
@@ -598,11 +597,23 @@ Invalid Variables</h3>
 	after substituting its ''var()'' functions,
 	is invalid.
 	When this happens,
-	the computed value of the property is either
-	the property's inherited value
-	or its initial value
-	depending on whether the property is inherited or not, respectively,
-	as if the property's value had been specified as the ''unset'' keyword.
+	the computed value is one of the following
+	depending on the property's type:
+
+	<dl class="switch">
+
+		:   The property is a non-registered [=custom property=]
+		:   The property is a [=registered custom property=]
+		    with [=univerisal syntax definition|universal syntax=]
+		::  The computed value is the <a>guaranteed-invalid value</a>.
+
+		:   Otherwise
+		::  Either the property's inherited value
+		    or its initial value
+		    depending on whether the property is inherited or not, respectively,
+		    as if the property's value had been specified as the ''unset'' keyword.
+
+		</dl>
 
 	<div class='example'>
 		For example, in the following code: