How does "use" work in waf?

[Hal Murray]

from ntpd/wscript:
        use="libntpd_obj isc ntp M parse RT CAP SECCOMP PTHREAD NTPD "
            "CRYPTO DNS_SD DNS_SD_INCLUDES %s SOCKET NSL SCF" % use_refclock,

What is the significance of being in uppercase?

How does waf handle libraries that aren't needed and may not be available?

Does PTHREAD get special handling?  man says:
         Compile and link with -pthread.
(-pthread vs -lpthread)


-- 
These are my opinions.  I hate spam.