Revise description to clarify that Array.map works on elements which are not missing, i.e. have been set and not deleted. It does work on elements set to `undefined`. See http://es5.github.io/#x126.96.36.199
3rd attempt: “`border-box` h & w props include c, p & b but not m. `content-box` h & w props include c but not p, b or m. `margin-box` h & w props include c, p, b & m. `padding-box` h & w props include c & p but not b or m.”
Revert to revision of 2015-02-26 11:27:07 by teoli: "My changes weren’t saved, so reverting to previous revision."
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