I'm unsure what exactly you're looking for.
For a technical overview how blending changes the graphics model, the
introduction from the pdf reference model is quite good [1]
Basically, I would like blending to be as easy as opacity (they are very
similar in behavior).
An author shouldn't have to know the technical details how blending works.
Instead, he should just be able to provide the blend mode on an element and
that element (and it's content) should blend with the backdrop, again just
like transparency.
Proposal to add markup so you can manually construct the backdrop will
prove very difficult to use and brittle.
I've seen numerous examples where authors try to mimic blending either by
rasterizing content to images in photoshop or by using transparency (which
can only approximate 'screen' and it also make the artwork dark).
1:
http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdfchapter
11.2
On Wed, May 22, 2013 at 12:02 AM, Robert O'Callahan <robert@ocallahan.org>wrote:
> It would still help if you could explain what the use-cases are.
>