Reset to the @when from the resolved-on proposal (w3c#6632)

which was chosen to avoid clashing badly with the @if in SASS

Author: tabatkins

css-conditional-4/Overview.bs

@@ -41,10 +41,10 @@ and supported font technologies.
 It also adds generalized conditional rules
 and chained conditional rules.
 
-It also adds an ''@if'' rule,
+It also adds an ''@when'' rule,
 which generalizes the concept of a conditional rule.
 Anything you can express in an existing conditional rule
-can be expressed in ''@if'',
+can be expressed in ''@when'',
 it just has to be wrapped in an appropriate function
 to declare what kind of condition it is.
 This allow authors to easily combine multiple types of queries,
@@ -104,15 +104,15 @@ when the text and layout processing engine ingesting
 this CSS text is capable of utilising the specified font-technology
 in layout and rendering.
 
-<h2 id="if-rule">Generalized Conditional Rules: the ''@if'' rule</h2>
+<h2 id="when-rule">Generalized Conditional Rules: the ''@when'' rule</h2>
 
-The <dfn>@if</dfn> at-rule is a <a>conditional group rule</a>
+The <dfn>@when</dfn> at-rule is a <a>conditional group rule</a>
 that generalizes the individual <a>conditional group rules</a>
 such as ''@media'' and ''@supports''.
 It is defined as:
 
 <pre class=prod>
-@if <<boolean-condition>> {
+@when <<boolean-condition>> {
 	<<stylesheet>>
 }
 </pre>
@@ -160,7 +160,7 @@ It is defined as:
 }
 </pre>
 
-''@else'' is interpreted identically to ''@if''.
+''@else'' is interpreted identically to ''@when''.
 If its <<boolean-condition>> is omitted,
 it's treated as having a condition that's always true.
 
@@ -189,7 +189,7 @@ An ''@else'' rule that is not part of a <a>conditional rule chain</a> is invalid
 	For example, here's a (somewhat silly) conditional chain:
 
 	<pre class="lang-css">
-		@if media(width >= 400px) and media(pointer: fine) and supports(display: flex) {
+		@when media(width >= 400px) and media(pointer: fine) and supports(display: flex) {
 			/* A */
 		} @else supports(caret-color: pink) and supports(background: double-rainbow()) {
 			/* B */
@@ -252,7 +252,7 @@ An ''@else'' rule that is not part of a <a>conditional rule chain</a> is invalid
   so will always be chosen unless one of the earlier conditions succeeds.
 
   <pre class="lang-css">
-  @if font-technology(color-COLRv1) and font-technology(variations) {
+  @when font-technology(color-COLRv1) and font-technology(variations) {
       @font-face { font-family: icons; src: url(icons-gradient-var.woff2); }
   }
   @else font-technology(color-SVG) {
@@ -272,7 +272,7 @@ An ''@else'' rule that is not part of a <a>conditional rule chain</a> is invalid
   and font variations are also supported.
 
   Notice too that only one of the available options will be downloaded;
-  this would not be the case without @if and @else,
+  this would not be the case without ''@when'' and ''@else'',
   as the next example shows.
 </div>
 
@@ -306,7 +306,7 @@ No Security issues have been raised against this document
 
 <h2 class=no-num id="acknowledgments">Acknowledgments</h2>
 
-The @if and @else rules are based on a proposal by Tab Atkins.
+The @when and @else rules are based on a proposal by Tab Atkins.
 
 <h2 id='changes' class='no-num'>
   Changes</h2>
@@ -317,7 +317,7 @@ The @if and @else rules are based on a proposal by Tab Atkins.
 
   <ul>
     <li>Added some examples</li>
-    <li>Added @if and @else per CSSWG resolution</li>
+    <li>Added @when and @else per CSSWG resolution</li>
     <li>Extended @supports feature to express font capabilities</li>
     <li>Added two co-editors per CSSWG resolution</li>
     <li>Added Privacy and Security sections</li>