resource naming

One question we keep bumping into, as on the last call, is what to call a
resource in the spine/reading order (whatever your preferred terminology
is).

 

Is "primary resource" good enough? Do we need something more descriptive,
like epub's "content document"?

 

The corollary question is do we need a name for all other resources to
clearly separate, and if so, what? Subresources?

 

Matt