Core Block is the union of the fifteen built-in block types (Paragraph, Heading, Code, Math, Image, Video, File, Button, Embed, WebEmbed, Nostr, Table, TableRow, TableColumn, Query). It is the strict core Hypermedia defines. Anyone can extend it by making a larger union that includes it plus their own block types.

The Seed app also knows Slot (an invisible container for top-level lists and grids), Link (a navigation menu item) and the legacy Group, which are not part of this union. Anything else still parses as the open block. Blocks has one line per type, with its attributes.

See also

Blocks: every built-in type with its attributes.

block: the open block that accepts unknown types.

block/base: the base a new type extends.

Example: app block: a larger union that includes the core.