The related material block covers data Groups P.22 and P.23, providing links to related works and related products. The block as a whole is optional and non-repeating.

None of the individual sections are mandatory within an occurrence of the block. However, in most circumstances, the block should contain at least one instance of <RelatedWork> or <RelatedProduct>. It may be empty only within a partial or ‘block update’ (Notification or update type 04, see P.1.2), when the intention is to remove all previously-supplied information about related works and products.