posix standards? $(CURDIR) or $$PWD or $(shell pwd)?

[gk]

I am trying to write makefiles that are least dependent on a particular make.
The Gnu make manual says:

>The make programs in various other systems support a few features that 
are not implemented in GNU make. The POSIX.2 standard (IEEE Standard 
1003.2-1992) which specifies make does not require any of these features.

Does this imply that Gnu make is POSX.2 compliant and contains no non-POSIX 
features?

In particular, I would like to know which is better: $(CURDIR) or $$PWD or 
$(shell pwd)?
Is $(CURDIR) supported by all makes, or at least by POSIX?

Where can I find 'posix standard' for make? It appears to not be freely 
available. It is apparently only a 40 page document: I have seen it on 
techstreet.com for the price of $51 hardcover; $107 for PDF version.

Standard            Read about Tracking...
                           IEEE Standards Interpretations for IEEE Std. 
1003.2-1992 : March
                           1994 Edition
                           Document Number: IEEE 1003.2-1992
                           Institute of Electrical and Electronics Engineers
                           01-Jan-1994
                           ISBN: 155937411X
                           40 pages

Thanks,
Greg Keraunen <address@hidden>