There has been some confusion about how the sidebar works in Projects. This is an attempt to describe in a short, clear paragraph. A more detailed explanation (in particular with respect to motivation) of the sidebar is available at SidebarSpec2.

The sidebar is primarily a navigation affordance. It is comprised of two parts

1. A horizontal applications bar (or Appbar for short) and
2. A vertical list of collections

The two parts work in concert to aid in navigation.

The vertical list of collections are conceptually-based groupings of items irrespective of Kind. (ie. All my items, All incoming items, All outgoing items, All trash items, All items related to Home, All items related to Work, etc)

The horizontal Appbar puts Kind-based lenses on the vertical list of collections. The most generous lens is the All (or All Kinds) lens, which is to say that when the user is in the All lens, there is no lens being applied to the sidebar.

When the user applies the Mail lens, the vertical list of collections in the sidebar are filtered down to only display mail items. (ie. All my items turns into All my mail, All items related to Home turn into All email related to Home) The same applies when applying the Task and Calendar lenses.

To help users understand that the Appbar is simply a series of lenses, the vertical list of collections in the sidebar provide visual feedback in various forms.

• The name of the All collection changes to reflect the lens. ie. All my items becomes All my tasks.
• The icon next to the All collection changes to match the icon of the selected lens in the Appbar.
• Collections that end up with 0 items as a result of a lens being applied grey out. If the user tries to click on a greyed out collection, they are given a textual explanation of why the collection has been greyed out. ie. The home collection does not contain any tasks.
• The unread message counts next to each collection adjust to reflect the lens. (ie. There are only 34 unread tasks in the Home collection out of a total of 68 unread items in the Home collection.)

The underlying motivation for the orthogonal design of the sidebar is the realization that users often want to see their information from multiple perspectives, most notably by Kind and by some organizational scheme over their own device (ie. projects, categories, topics, etc).

Current PIMs (ie. Entourage Project Center) have addressed this need by adding yet another application area where users can pull together items of various kinds into cross-kind projects that are in addition to 1) the kind-specific organizational affordances already in place (ie. Folders, Task lists, Calendars) and 2) cross-kind categories. All of this UI just so users can sometimes see things by project and other times see things by kind. All this UI that makes it hard for users to use because it takes too much effort to understand what all these different features do, how they relate together and how to set them up.

In Chandler, we're hoping to offer a simpler way to slice and dice information by unifying all of these different organizational affordances in a single notion of collection which users can then view via different kind-based lenses.