[cairo] surface SVG to current context

[Donn]

> Yes, Carl did that. But he was using poppler respective rsvg, libraries
> which are outside the scope of cairo.

So, it seems the only purpose for having a "Surface" as an input to the Source 
is for feedback from a push/pop_group.

 The "input" point for external SVG/PDF files is via librsvg/poppler and into 
the current context.

I'll emend the diagram to cover this.

I still have not had the courage to look at create_similar and company, 
hopefully the concepts I have now will stand up to them!

> A cairo surface is output only. The fact that it can be used as input is
> purely coincidental (and is part of the non-obviousness of cairo)
That's what I'm trying to clear-up. I wait for snippets of clarity from this 
list like a parched man in the Kalahari! Thanks for your info!

> What I still think is missing is some way to serialize / deserialize a
> stream of cairo commands into a file, which is part of cairo, basically a
> meta file system.
Carl has mentioned this. I can't really understand it all. In my mind I see 
that "reading" an SVG file and "writing" an SVG file are two sides of the 
same (horribly complex, no doubt) coin. It's all about parsing XML and then 
element strings. So, I'll wait and see what this meta file stuff is all 
about.

\d