[racket] linking to PLaneT package documentation from Scribble

What's the best way, from Scribble documentation of a PLaneT package,  to:

1. Make a hyperlink to the documentation of a different PLaneT package, 
*without* having a PLaneT dependency on that package?  (I see "secref 
#:doc"...)

2. Make a hyperlink to the documentation for a particular identifier 
within a different PLaneT package, ideally without having a dependency 
on that package?  (It's OK if they are broken links if the other package 
is not installed, or perhaps they could fail over to the documentation 
on "planet.racket-lang.org".)

3.In Racket code examples, have identifiers from a different PLaneT 
package be links to the documentation for those identifiers in that 
different PLaneT package?  (Again, ideally without having a dependency 
on that package.)  (This is merely a nice-to-have feature, not really 
necessary.)

Also, another consideration:

4. How do versions of PLaneT packages affect the above answers?  (Can we 
specify minimum minor versions in our hyperlinks?)

Motivation for these questions: I'm trying to release a handful of 
loosely-coupled SXML-related PLaneT packages, and I want the 
documentation for some of the packages to link to the documentation for 
some of the other packages.  At the same time, I don't want these 
documentation links to turn into hard dependencies that pull in PLaneT 
packages solely for the purposes of getting links right in the formatted 
documentation.

Rather than experiment, perhaps someone knows offhand the best ways.

-- 
http://www.neilvandyke.org/