[TASK] Mark the public class constants as @internal

src/Parsing/ParserState.php

@@ -9,6 +9,8 @@ class ParserState
 {
     /**
      * @var null
+     *
+     * @internal
      */
     public const EOF = null;
 

src/Property/AtRule.php

@@ -12,13 +12,17 @@ interface AtRule extends Renderable, Commentable
      * we’re whitelisting the block rules and have anything else be treated as a set rule.
      *
      * @var string
+     *
+     * @internal
      */
     public const BLOCK_RULES = 'media/document/supports/region-style/font-feature-values';
 
     /**
      * … and more font-specific ones (to be used inside font-feature-values)
      *
      * @var string
+     *
+     * @internal
      */
     public const SET_RULES = 'font-face/counter-style/page/swash/styleset/annotation';
 

src/Property/KeyframeSelector.php

@@ -8,6 +8,8 @@ class KeyframeSelector extends Selector
      * regexp for specificity calculations
      *
      * @var string
+     *
+     * @internal
      */
     public const SELECTOR_VALIDATION_RX = '/
     ^(

src/Property/Selector.php

@@ -49,6 +49,8 @@ class Selector
      * regexp for specificity calculations
      *
      * @var string
+     *
+     * @internal
      */
     public const SELECTOR_VALIDATION_RX = '/
         ^(