Rename method to renderNonConditionalAtRules

This clarifies that not all at-rules are rendered.  Also rename the associated
property, and add note in the DocBlock for the method that `@charset` rules are
discarded.

src/CssInliner.php

@@ -1080,7 +1080,7 @@ private function removeUnsupportedOfTypePseudoClasses(string $selectorPart): str
      */
     private function copyUninlinableCssToStyleNode(CssDocument $cssDocument): void
     {
-        $css = $cssDocument->renderAtRules();
+        $css = $cssDocument->renderNonConditionalAtRules();
 
         // avoid including unneeded class dependency if there are no rules
         if ($this->getMatchingUninlinableCssRules() !== []) {

src/Utilities/CssDocument.php

@@ -41,7 +41,7 @@ class CssDocument
      *
      * @var string
      */
-    private $atRules;
+    private $nonConditionalAtRules;
 
     /**
      * @param string $css
@@ -53,7 +53,7 @@ public function __construct(string $css)
             = $this->extractImportAndCharsetRules($cssWithoutComments);
         [$this->styleRules, $cssAtRules]
             = $this->extractNonConditionalAtRules($cssWithoutCommentsCharsetOrImport);
-        $this->atRules = $cssImportRules . $cssAtRules;
+        $this->nonConditionalAtRules = $cssImportRules . $cssAtRules;
     }
 
     /**
@@ -93,13 +93,14 @@ public function getStyleRulesData(array $allowedMediaTypes): array
 
     /**
      * Renders at-rules from the parsed CSS that are valid and not conditional group rules (i.e. not rules such as
-     * `@media` which contain style rules whose data is returned by {@see getStyleRulesData}).
+     * `@media` which contain style rules whose data is returned by {@see getStyleRulesData}).  Also does not render
+     * `@charset` rules; these are discarded (only UTF-8 is supported).
      *
      * @return string
      */
-    public function renderAtRules(): string
+    public function renderNonConditionalAtRules(): string
     {
-        return $this->atRules;
+        return $this->nonConditionalAtRules;
     }
 
     /**

tests/Unit/Utilities/CssDocumentTest.php

@@ -269,7 +269,7 @@ public function rendersValidNonConditionalAtRule(string $atRuleCss, string $cssB
     {
         $subject = new CssDocument($cssBefore . $atRuleCss);
 
-        $result = $subject->renderAtRules();
+        $result = $subject->renderNonConditionalAtRules();
 
         self::assertStringContainsString(\trim($atRuleCss), $result);
     }
@@ -307,7 +307,7 @@ public function rendersMultipleNonConditionalAtRules(string $cssBetween): void
     {
         $subject = new CssDocument('@import "foo.css";' . $cssBetween . self::VALID_AT_FONT_FACE_RULE);
 
-        $result = $subject->renderAtRules();
+        $result = $subject->renderNonConditionalAtRules();
 
         // The content of the rendered rules is covered by other tests.  Here just check the number of rendered rules.
         self::assertSame(2, \substr_count($result, '@'));
@@ -338,7 +338,7 @@ public function discardsAtCharsetRule(): void
     {
         $subject = new CssDocument('@charset "UTF-8";');
 
-        $result = $subject->renderAtRules();
+        $result = $subject->renderNonConditionalAtRules();
 
         self::assertSame('', $result);
     }
@@ -355,7 +355,7 @@ public function notRendersInvalidNonConditionalAtRule(string $atRuleCss, string
     {
         $subject = new CssDocument($cssBefore . $atRuleCss);
 
-        $result = $subject->renderAtRules();
+        $result = $subject->renderNonConditionalAtRules();
 
         self::assertThat(
             \trim($result),
@@ -396,7 +396,7 @@ public function notRendersAtMediaRule(): void
     {
         $subject = new CssDocument('@media screen { p { color: red; } }');
 
-        $result = $subject->renderAtRules();
+        $result = $subject->renderNonConditionalAtRules();
 
         self::assertSame('', $result);
     }