[TASK] Mark OutputFormat as not extendable (#1131)

Also mark the constructor as `@internal`.

Co-authored-by: JakeQZ <[email protected]>

Author: oliverklee

CHANGELOG.md

@@ -21,6 +21,7 @@ Please also have a look at our
 
 ### Changed
 
+- Mark the `OutputFormat` constructor as `@internal` (#1131) 
 - Mark `OutputFormatter` as `@internal` (#896)
 - Make `Selector` a `Renderable` (#1017)
 - Mark `Selector::isValid()` as `@internal` (#1037)
@@ -35,6 +36,7 @@ Please also have a look at our
 
 ### Deprecated
 
+- Deprecate extending `OutputFormat` (#1131)
 - Deprecate magic method forwarding from `OutputFormat` to `OutputFormatter`
   (#894)
 - Deprecate greedy calculation of selector specificity (#1018)

src/OutputFormat.php

@@ -4,6 +4,9 @@
 
 namespace Sabberworm\CSS;
 
+/**
+ * Extending this class is deprecated in version 8.8.0; it will be made `final` in version 9.0.0.
+ */
 class OutputFormat
 {
     /**
@@ -180,6 +183,9 @@ class OutputFormat
      */
     private $indentationLevel = 0;
 
+    /**
+     * @internal since V8.8.0. Use the factory methods `create()`, `createCompact()`, or `createPretty()` instead.
+     */
     public function __construct() {}
 
     /**