Okay, maybe everyone else already knows this, but it was news to me (thanks Paul P and Soundwise).
 
Here's an example SFZ file, with the relevant parts bolded. In this example, the keyswitch range is C2 to B2. The first region will sound if you press C2, and the second region will sound if you press D2.
 
sw_lowkey=C2
sw_hikey=B2

<region> pitch_keycenter=c3 lokey=c3 hikey=C4 sample=SyntronicGuitars\ChordPads_C3.flac sw_down=C2
<region> pitch_keycenter=f#4 lokey=C3 hikey=C4 sample=SyntronicGuitars\Harmonics_B4.flac sw_down=D2

That is plain awesome! I'm working on new instruments for RPro, and this news came in just the right time. Thank you, Craig and Paul P!

Cool! Speaking of which...I just realized the folder names in the SFZ file give a hint about what an upcoming expansion pack is going to be. 

 
Thanks for trying this out and sharing it with us, Craig.  I've been hoping for a long time that this was possible but hadn't yet gotten around to trying.
 

Anderton
Cool! Speaking of which...I just realized the folder names in the SFZ file give a hint about what an upcoming expansion pack is going to be. 

SyntronicGuitars, can't wait!
 
 
Since Rapture Pro has a preview keyboard strip we should all put in a feature request to have the KeySwitches appear on it.

chad
Since Rapture Pro has a preview keyboard strip we should all put in a feature request to have the KeySwitches appear on it.

Does it already show mapped keys ?  If not it would also be nice if it did, like in DropZone.

Interesting. 
 
I do wish that the makers of synths that support SFZ would get it into their heads that documenting just what aspects of SFZ are supported is pretty damn important.  The SFZ spec is huge and complicated.  No synth comes anywhere close to supporting all the features. 
 
So what's the poor user to do?  Try everything and compile their own list of what works and what doesn't?  The developer with access to the code could put such a list together with little effort.  Alchemy (1) was the only synth I've ever encountered that bothered to document what SFZ features were supported.

 
Unfortunately, from my point of vue, sfz as a standard is more or less dead.
 
So, if one is planning to learn sfz, it would be a good idea to start with the very basics and make sure that works.  Then just go through the spec and add functions one at a time.  You have to do that anyway to really learn the language.
 
René's sfzFormatTestSuite_001 might also be a good place to start.
 

Paul P
 
Unfortunately, from my point of vue, sfz as a standard is more or less dead.
 

Cannot agree with that.  Plenty of current synths support SFZ to some extent (although almost none of them document just what features are supported).  The brand new UVI Falcon, which a lot of folks are calling the synth of the year, supports SFZ as an input format.  Of course, its documentation once again does not say how much of the spec is supported. 

dmbaer

Paul P
 
Unfortunately, from my point of vue, sfz as a standard is more or less dead.
 

Cannot agree with that.  Plenty of current synths support SFZ to some extent (although almost none of them document just what features are supported).  The brand new UVI Falcon, which a lot of folks are calling the synth of the year, supports SFZ as an input format.  Of course, its documentation once again does not say how much of the spec is supported. 

That's what I meant .  Either everyone supports everything in a standard, or various subsets of a standard are defined and agreed to (we called them Application Profiles back in the day).  I don't believe any producers of sfz compliant instruments have agreed on anything.  So, with respect to sfz being a standard, it isn't.