The difference between cl-* and cl-*-<implementation> ports

[Kero-Chan]

Hi,

Can someone explain to me what is the difference between cl-* and
cl-*-<implementation> ports?
Like cl-ppcre and cl-ppcre-{cmucl|sbcl|clisp}?
I looked at the Makefiles, but it's still not clear :(
Esp., considering theese are *ports*: Looking at the description of,
say, cl-ppcre-clisp:
"This package installs binaries for CLISP."
I don't really understand this. CLISP is actually a bytecode
interpreter. So I guess this installs multiplatform bytecode binaries?
But... this is a *port*! Packages install binaries; ports download the
source and compile it.

Thanks...
/Kero-Chan/