Source

File: wp-includes/class-wp-theme.php

public function offsetExists( $offset ) {
		static $keys = array(
			'Name',
			'Version',
			'Status',
			'Title',
			'Author',
			'Author Name',
			'Author URI',
			'Description',
			'Template',
			'Stylesheet',
			'Template Files',
			'Stylesheet Files',
			'Template Dir',
			'Stylesheet Dir',
			'Screenshot',
			'Tags',
			'Theme Root',
			'Theme Root URI',
			'Parent Theme',
		);

		return in_array( $offset, $keys, true );
	}