Views are the primary source of information for the client (player) of the simulated world.
By default, if no views are generated and sent to a player, this player won't see a thing, not even hers objects (be they ships, planets, cars...).
By using views the game designer can ensure that the client program (and thus the player) knows only the necessary. Of course one can give any type of information in a view, be it detailed or very superficial.
Let us say that by default an Airplane sees every shape moving in the air in a radius of 50 miles. So the basic airplane will send its owner a view for every object in this radius. This view can contain coordinates and apparent shape/size/heading.
With a more precise device (for example a radar, and following a DoAScan command) the view sent back to the player could be more specific (exact heading, speed, mass).
Information passed with a view does not follow a particular syntax. It is up to the client to understand them and display them to the player in a readable form. Views are just collections of pairs <name, value>.
PbML does not cover, so far, client programs. It just offers tools to interact with the client program, and specifies only the protocol of interaction, i.e. the format of the files sent back and forth between clients and the server.
Please see chapter 7 on the details of this interaction.