As you can see, they can be nested objects. There are a few limitations that you
should be aware of:
Documents cannot have a top-level key by the name of "key". This is reserved
for storing the document key.
Documents cannot have keys with a "." in them. This is because the "." is the
seperator chosen for nested objects in
expressions.
Documents cannot have arrays in them. This is a design decision to force users
like you to normalize data. Please just normalize data, denormalization is an
awful bug-ridden paradigm.