attributes editable in DW templates

When making an attribute editable, I noticed that sometimes the attribute is
written as @@(_document['attributename'])@@, and sometimes simply as
@@(attributename)@@. I assume they're both correct and that one is an absolute
path and the other a relative path (??). Am I correct in that assumption?

I was just curious when DW decides when to write one over the other. I haven't
varied how I apply the attributes (I don't think), but it seems to randomly
choose how it is written.

Also, just for my own knowledge, is this using XML (which I know nothing
about, but hope to soon) to create the editable attributes

Thanks,
Paul