Re-add as a valid value to applicable preferences

index.bs

@@ -107,6 +107,7 @@ This is modeled after the `prefers-contrast` user preference media feature as de
     1. Let |validValues| be a new empty [=sequence=].
     1. Add `"more"` to |validValues|.
     1. Add `"less"` to |validValues|.
+    1. Add `"no-preference"` to |validValues|.
     1. Return |validValues|.
 </div>
 
@@ -128,6 +129,7 @@ This is modeled after the `prefers-reduced-motion` user preference media feature
 
     1. Let |validValues| be a new empty [=sequence=].
     1. Add `"reduce"` to |validValues|.
+    1. Add `"no-preference"` to |validValues|.
     1. Return |validValues|.
 </div>
 
@@ -149,6 +151,7 @@ This is modeled after the `prefers-reduced-transparency` user preference media f
 
     1. Let |validValues| be a new empty [=sequence=].
     1. Add `"reduce"` to |validValues|.
+    1. Add `"no-preference"` to |validValues|.
     1. Return |validValues|.
 </div>
 
@@ -168,6 +171,7 @@ This is modeled after the `prefers-reduced-data` user preference media feature a
 
     1. Let |validValues| be a new empty [=sequence=].
     1. Add `"reduce"` to |validValues|.
+    1. Add `"no-preference"` to |validValues|.
     1. Return |validValues|.
 </div>
 
@@ -232,10 +236,6 @@ interface PreferenceObject : EventTarget {
     1. Return |validValues|.
 </div>
 
-Note: "no-preference" is deliberately not an allowed value for any preference.
-This is to mitigate the risk of sites misusing the API to the detriment of user experience.
-Authors should instead clear the preference override. See [#30](https://github.com/WICG/web-preferences-api/issues/30) for more details.
-
 ### {{onchange}} event handler attribute ### {#onchange-attribute}
 
 The <dfn attribute for=PreferenceObject>onchange</dfn> attribute is an [=event handler IDL attribute=] for