A space can be part of another: a working group within a project, a project within an organisation. This is declared with gen:isSubSpaceOf, either in the space's own definition or as a separate nanopublication. The link counts only when an admin of each space stands behind it — one person who is admin of both, or a declaration from each side — so no space can attach itself to another uninvited.

Sub-spaces are shown on the parent's page and the parent on the sub-space's page, but membership does not flow between them: being a member of the parent says nothing about the sub-space, and the other way round.