The Content detail block comprises the single data Group P.18. The block as a whole is non-repeating. It is not mandatory within the <Product> record, and is used only when there is a requirement to describe individual chapters or parts within a product in a fully structured way. The more usual ONIX practice is to send a table of contents as text, possibly in XHTML, in Group P.14.

When used, the block should normally contain at least one instance of <ContentItem>. 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 content detail.