[cairo] Observations from a newb

[Donn]

Sorry if I ask silly questions, but I do not savvy the "source" concept yet. I 
can see that it's a place where data comes from, but not how the flavours, of 
what a source can be, work. 
 I sort of picture a source as being an array of rgba values that have been 
preset in memory from some other place (the source of the source). So it's 
hard to picture how a source can said to be SVG or PDF, given my oddball 
angle on it.
 For example, I assume one would use librsvg to open an SVG file and then some 
cairo footwork would turn that into a source; after that it can be stamped 
around as per the clever cairo idiom. But how does this source differ from a 
bitmap? I mean, what are it's properties that differentiate it? Can it be 
smoothly scaled for example (i.e. redrawn as a vector and then updated across 
the cairo surface wherever it has been used). 

Am I on the right track?

\d