CSS's shorthand order — (all), (vertical, horizontal), or all four
clockwise from the top — because that is the order every author already
knows, and none of the four is more fundamental than the others.
Optionaltop: numberOptionalright: numberOptionalbottom: numberOptionalleft: numberDistance from the bottom edge.
Distance from the left edge.
Distance from the right edge.
Distance from the top edge, in layout units.
left + right — the horizontal space these insets consume.
top + bottom — the vertical space these insets consume.
Symmetric edge insets in layout units — padding and margins (§74).
A mutable class rather than an object literal, for plan D7's reason: insets are read every layout pass, so they are written in place (
set,setAll,copy) and never replaced.