7 files declare their use of ExtensibleParserInterface in Markdown 8.2

AllowedHtmlManager.php in src/PluginManager/AllowedHtmlManager.php

BaseExtension.php in src/Plugin/Markdown/CommonMark/BaseExtension.php

ExtensionCollection.php in src/PluginManager/ExtensionCollection.php

FootnoteExtension.php in src/Plugin/Markdown/CommonMark/Extension/FootnoteExtension.php

HeadingPermalinkExtension.php in src/Plugin/Markdown/CommonMark/Extension/HeadingPermalinkExtension.php

ParserConfigurationForm.php in src/Form/ParserConfigurationForm.php

ParserManager.php in src/PluginManager/ParserManager.php