The updates a watcher must fire on for a document write to start
definition: the fields its start.filter reads off the written document.
A definition with no start.filter, or one reading none of the document's
own fields but _type, gets noUpdate. A filter whose truth can change
without a write to the subject gets everyUpdate: one reading the document
in a way no field path describes, such as the whole document or a field named
by an expression; one reading any other document, through a dataset scan or a
dereference; and one reading the clock, $now.
The updates a watcher must fire on for a document write to start
definition: the fields itsstart.filterreads off the written document.A definition with no
start.filter, or one reading none of the document's own fields but_type, getsnoUpdate. A filter whose truth can change without a write to the subject getseveryUpdate: one reading the document in a way no field path describes, such as the whole document or a field named by an expression; one reading any other document, through a dataset scan or a dereference; and one reading the clock,$now.