Incorrect and unclear description of `prev_batch` usage for /sync

From the spec:

Finally, the response includes, for each room, a prev_batch field, which can be passed as a start parameter to the /rooms/<room_id>/messages API to retrieve earlier messages.
[...]
prev_batch: A token that can be supplied to the from parameter of the rooms/{roomId}/messages endpoint.

Two issues with this:

1. It's not clearly defined what dir one should request from /messages, using this prev_batch token
2. There is no such thing as a start parameter, like the first part of the quoted text claims (there's only such a property in the response); presumably, that was supposed to say from rather than start.

Open the specification section linked in the issue and locate the /sync room prev_batch description alongside the rooms/{roomId}/messages parameter documentation. Check the parameter names and determine how the required dir value should be documented; done means the text is accurate and unambiguous.