What does "file link" do in Shadowplan?

All,

I'm in the process of adding tags to all my Shadowplan actions, and I 
noticed the "file link" action on the "Link" pop-up box.  What does 
that allow me to do?

Here's what I'd like it to do.  Using the GTD approach, I have a 
number of projects I've created in Shadowplan.  Of course, each 
project has a number of steps with different contexts.  For example, 
a home improvement project involves developing project designs and 
getting my wife's approval (of course) at home, yet buying the 
materials is an errand.  When I go to the Home Improvement store, 
i.e., I run my errand, I'd like to buy everything I've found I need 
for the Home Improvement store while I'm there.  (There's nothing 
worse than sinking all that travel time only to get back from a store 
and realize you needed one thing for another project!)  I'd like to 
have all my Errands exported to a single, updating list so when I 
went to the Home Improvement store I could simply sort that list by 
the Home Improvement tag and see everything I need to buy @ that 
store across all my Shadowplan lists.  Any help out there?

Thanks!

iiracing