Source

File: wp-includes/wp-db.php

public function __set( $name, $value ) {
		$protected_members = array(
			'col_meta',
			'table_charset',
			'check_current_query',
		);
		if ( in_array( $name, $protected_members, true ) ) {
			return;
		}
		$this->$name = $value;
	}