Actual pdf layers (aka "optional content")?

Has anyone considered implementing support for these in pgf? IMHO, the
main application would be beamer, where you wouldn't have to make each
frame a page. The trouble with the current approach is that
positioning is not that accurate, so the contents of a slide sometimes
"bobs" around with each frame; this is quite disturbing visually for
the audience. Some of my colleagues prefer PowerPoint to beamer for
this very reason.

There's a commercial package that supports PDF layers, but it also
depends on distiller. But pdftex 1.4 has had support for actual pdf
layers for quite a while now... pdftex 1.5.0 will also support merging
layers from included pdfs.

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