Added URL to page through items in the opposite direction of next_url…

…. The terminology is confusing here and maybe should be postponed until after 1.1.

pages/version/1.1.markdown

@@ -71,6 +71,8 @@ After that there’s an array of objects — `items` — that describe each obje
 
 * `next_url` (optional, string) is the URL of a feed that provides the next n items, where n is determined by the publisher. This allows for pagination, but with the expectation that reader software is not required to use it and probably won’t use it very often. `next_url` must not be the same as `feed_url`, and it must not be the same as a previous `next_url` (to avoid infinite loops).
 
+* `previous_url` (optional, string) is the URL of a feed that provides the previous n items in a paginated feed, complementing `next_url`. Because feeds often contain items in reverse-chronological order, `previous_url` references items that are usually _forward_ in time. They could be newer than the items at `feed_url` and `next_url`.
+
 * `icon` (optional, string) is the URL of an image for the feed suitable to be used in a timeline, much the way an avatar might be used. It should be square and relatively large — such as 512 x 512 — so that it can be scaled-down and so that it can look good on retina displays. It should use transparency where appropriate, since it may be rendered on a non-white background.
 
 * `favicon` (optional, string) is the URL of an image for the feed suitable to be used in a source list. It should be square and relatively small, but not smaller than 64 x 64 (so that it can look good on retina displays). As with `icon`, this image should use transparency where appropriate, since it may be rendered on a non-white background.