Add comment to PropertyAccessor interface

src/Mapping/PropertyAccessors/PropertyAccessor.php

@@ -4,7 +4,17 @@
 
 namespace Doctrine\ORM\Mapping\PropertyAccessors;
 
-/** @internal */
+/**
+ * A property accessor is a class that allows to read and write properties on objects regardless of visibility.
+ *
+ * We use them while creating objects from database rows in {@link UnitOfWork::createEntity()} or when
+ * computing changesets from objects that are about the written back to the database in {@link UnitOfWork::computeChangeSet()}.
+ *
+ * This abstraction over ReflectionProperty is necessary, because for several features of either Doctrine or PHP, we
+ * need to handle edge cases in reflection at a central location in the code.
+ *
+ * @internal
+ */
 interface PropertyAccessor
 {
     public function setValue(object $object, mixed $value): void;