debugfs question: What does "expand" do?

[Charles Riley <criley erad com>]

Hi,

What does the "expand_dir" command do in debugfs?
All the information I can find on it just says "Expand the directory 
filespec"
I googled the archives and can't find a post where someone actually used 
it to give me some context.
If I try it in debugfs (image opened ro) it seems to want to write to 
the image.

I'm having a bit of a stack underflow here, please help.
Thanks in advance,

Charles