Accession v. Accessory

What is the difference between accession and accessory? Article 440 of the Civil Code of the Philippines defines accession.

Accession is the right by virtue of which the owner of a thing becomes the owner of everything which is produced thereby, or which is incorporated or attached thereto, either naturally or artificially. Accessories are things joined to or included with the principal thing for the latter’s embellishment, better use, or completion.