appropriate containers, remove misleading const qualifiers, reduce
repeated XML walking.
(nw) Groups aren't parameterised, so they aren't as useful as they could
be (yes, it's on my TODO list). However, it's already useful for
putting a common set of elements in multiple views, potentially at
different locations/scales. See intlc44.lay and intlc440.lay for
examples of the level of copypasta this can eliminate. Be aware that
groups with explicit bounds don't clip thair content, it's only used for
calucating the transform matrix.
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