William Adams writes:
 > On Mar 9, 2011, at 5:38 AM, Frank Mittelbach wrote:
 > > Now you can say that if somebody starts of  the document with
 > > 
 > > \usepackage{expl3,xparse,template} 
 > > 
 > > say then everything will be fine whether or not the document will be produced
 > > by ordinary 2e format or 2x.
 > > 
 > > But history will tell us that what is likely to happen is that people start
 > > writing documents that will not \RequirePackage/\usepackage
 > Would it be possible to build the format in such a way that the packages in
 > question are built into it, but not activated unless such line(s) were
 > present in the document? 

I would say yes, though it needs a little thought (yes something is possible Philipp)

 > The check will be quick enough that we'd still save the half-second or so
 > per document, no? 

yep. This is what I hinted at with perhaps even making latex2x the recommented
format where expl3 would sit inside but without doing (hopefully) any harm to
2e documents that don't need it

 > Would there need to be an ``\activatepackage'' command? Or is there some
 > better command which should be used in LaTeX3? I've complained in the past
 > of LaTeX2e document pre-ambles being meaningless line-after-line of
 > \usepackage{foo} and would really like to see a nicer interface here ---
 > would this be a good opportunity to introduce it? 

as I said that would need a little thought and I would rather like to see some
serious thought put into it instead of hacking some stupid interface that one
regrets later.

I'm not so sure about your complaint about meaningless line-after-line
\usepackages, though. I was and is a simple interface but at least it ended up
with a clean specifcation what that particular 2e document needed.

But yes, why not something better ... but then first step would be to come up
with suggestions what a "better" interface would be