I thought I'd bring this to the attention of the group, in case you haven't
already seen it. Apple has published an iPhone Human Interface Guidelines
document. You can see it here:
I only skimmed through it, but I didn't see too much that was
Metaphor is an important concept in computer system design as well as in
language. Metaphor is more than just a literary device used for poetic
effect, it is an integral part of our language and thought.
Has anyone seen effective UI widgets for selecting an exact number of
choices greater than 1? Radio buttons do this for 1, but it seems we have
no standard for "Select two and only two choices."
writeboard.com does this for comparing two versions of a document you'd
like to compare. They use check boxes, and if a third choice is made the
UI unselects the other two.
Conceptually, an option I'm considering is like selecting two apples from
a pile of apples at the market, as you select them they are moved away
from the group.