Section [list.cons], paragraphs 6-8 specify that list assign (both forms) have the "effects" of a call to erase followed by a call to insert.

I would like to document that implementers have the freedom to implement assign by other methods, as long as the end result is the same and the exception guarantee is as good or better than the basic guarantee.

The motivation for this is to use T's assignment operator to recycle existing nodes in the list instead of erasing them and reallocating them with new values. It is also worth noting that, with careful coding, most common cases of assign (everything but assignment with true input iterators) can elevate the exception safety to strong if T's assignment has a nothrow guarantee (with no extra memory cost). Metrowerks does this. However I do not propose that this subtlety be standardized. It is a QoI issue.

Existing practise: Metrowerks and SGI recycle nodes, Dinkumware and Rogue Wave don't.