Help document the Panels 2 API (part 2)

This is task #2 of a two task project to document the extensive API in Panels 2. This task requires you to research and document the following sections of the Panels 2 API:

1) Document how to create a 'context' object using hook_panels_contexts()
2) Document how to create an argument for panels pages using hook_panels_arguments()
3) Document how to create a relationship from one context to another using hook_panels_relationships()
4) Document how to create a panel style using hook_panels_styles()

Documenting this might require searching through the Panels 2 code looking for module_invoke and $function() calls; the two hooks described above return a packet of data, and much of that data are pointers to functions that can be called. Describing that data and how those additional functions are used are key here. So beware that while there are only 4 steps listed above, each step is more complicated than it sounds.

Documentation for this task should be placed here: http://groups.drupal.org/node/7678 (This is a wiki page, so is easily edited)