[css-ui-4] Remove "do no impement" warning, replace with note

Closes w3c#1250

Author: frivoal

css-ui-4/Overview.bs

@@ -1749,17 +1749,37 @@ so this specification allows flexibility.
 
 <h3 id="appearance-switching" caniuse="css-appearance">Switching appearance</h3>
 
-<div class=issue>
-	<strong>This is a work-in-progress, not cleared for shipping</strong> (see <a href="https://github.com/w3c/csswg-drafts/issues/1250">Github issue 1250</a>).
+<pre class="propdef">
+Name: appearance
+Value: ''appearance/none'' | ''auto'' | ''button'' | ''textfield'' | ''menulist-button'' | <<compat-auto>>
+Initial: none
+Applies To: all elements
+Inherited: no
+Computed value: specified keyword
+Animation type: discrete
+</pre>
+
+While the way most elements in a document look can be fully controlled by CSS,
+controls are typically rendered by UAs using native UI controls of the host operating system,
+which can neither be replicated nor styled using CSS.
 
-	This previously existed as a prefixed form in most browsers.
+This specification introduces the 'appearance' property
+to provide some control over this behavior.
+In particular, using ''appearance: none'' allows authors
+to suppress the native style of controls,
+so that CSS can be used to restyle them.
+
+<details class=note>
+	<summary>Note on the history of this feature</summary>
+
+	This previously existed in prefixed form in most browsers.
 	Before standardization, in addition to none,
 	the possible values were a very long list of all the ways an element could look;
 	each value being responsible for giving form control their specific look and feel.
 	This list was different across browsers.
 
-	We concluded this was impractical to standardize,
-	in part because many apply to pseudo-elements that other browsers don't have,
+	The CSS Working Group concluded this was impractical to standardize,
+	in part because many values applied to pseudo-elements that other browsers don't have,
 	as they construct form elements differently,
 	and which should not be standardized,
 	since the ability to make for controls look substantially different on different platforms
@@ -1769,7 +1789,8 @@ so this specification allows flexibility.
 	into any (other) arbitrary form control
 	is considered a misfeature.
 
-	Instead, we'd just have an "auto" value that makes form controls look like whatever they need,
+	Instead, the design being specified
+	is based on just having an "auto" value that makes form controls look like whatever they need,
 	and a "none" value that suppresses "native" look.
 
 	However, there is evidence that this alone is not web compatible,
@@ -1779,49 +1800,17 @@ so this specification allows flexibility.
 	input[type=checkbox] { appearance: checkbox; }
 	</code></pre>
 
-	This Work-In-Progress specification is a compromise between the two,
+	The design specified here is a compromise between the two,
 	preserving the simplicity of the ''none | auto'' model
-	while maintaining compatibility with existing content.
-</div>
-
-While the way most elements in a document look can be fully controlled by CSS,
-controls are typically rendered by UAs using native UI controls of the host operating system,
-which can neither be replicated nor styled using CSS.
-
-This specification introduces the 'appearance' property
-to provide some control over this behavior.
-In particular, using ''appearance: none'' allows authors
-to suppress the native style of controls,
-so that CSS can be used to restyle them.
-
-<pre class="propdef">
-Name: appearance
-Value: ''appearance/none'' | ''auto'' | ''button'' | ''textfield'' | ''menulist-button'' | <<compat-auto>>
-Initial: none
-Applies To: all elements
-Inherited: no
-Computed value: specified keyword
-Animation type: discrete
-</pre>
-
-<div class="note">
-	Note: This specification intentionally refrains from making the appearance
-	of all possible form controls and sub-controls available as values,
-	as had previously been attempted by earlier proposals for this property
-	and by several UA vendors in experimental implementations.
-	Experience has shown that such a list would be very long and not practical to maintain,
-	and UAs would need to add non-standard values
-	to account for the behavior of non-standard pseudo-elements
-	sometimes used to implement form controls.
-	Moreover, many values of such an enumeration only make sense
-	on a single element or pseudo-element,
-	and are never used outside of the UA stylesheet.
-	The ability provided by this approach to turn any arbitrary element
-	into any arbitrary form control or subcontrol
-	was also a significant source of complexity,
-	despite being not particularly useful.
-	The model provided by this specification is deliberately simpler.
-</div>
+	while maintaining compatibility with existing content
+	via a few additional keywords.
+
+	The precise list of keywords needed for compatibility
+	and their exact behavior
+	is likely to be refined in future version of this specification
+	to better handle compatibility with existing content.
+	The CSS-WG welcomes relevant feedback.
+</details>
 
 <dl dfn-type=value dfn-for=appearance>
 	<dt><dfn>none</dfn>