Halliday & Matthiessen (2004: 471):
A fact clause serving as Head in a nominal group without a fact noun can be related to the first class of fact noun — that of ‘cases’, since such a fact clause is always agnate with an expanded nominal group with fact as Head. Whether the nominal group has a fact noun as Head or not, the fact clause is embedded. Because there is no projecting process involved, to which it could be paratactically or hypotactically related, a fact can appear on in embedded form: either as Qualifier to a ‘fact’ noun, or as a nominalisation on its own.