Sibling nodes are not supported
Currently only T-like navigation path is supported: the horizontal line is "sections" (the top level) and the vertical is the path from a section to current document.
This is enough in most cases but in some sibling nodes of the vertical line would be very useful. For example, current position is a blog post, the active section is "Blog" and the whole path looks like this:
( ("Home", "Blog", "About"), "2009", "February", "Some Post" )
It would be nice to click/hover on "February" and get a dropdown menu with all months; the same with "2009" -- the user wants all relevant years to be listed.
Maybe some more complex controls could be introduced for handling ranges (e.g. "1st week", "low price: $xx..$xxx", etc.).
The problem here is that there can be too many sibling nodes on some levels or these levels can be generated (e.g. date parts), so special callbacks for siblings should be introduced. This requires some thinking. =)
A straighforward implementation would suffice to start with.