@node Compliance to Standards
@appendix GNUstep Compliance to Standards
@cindex standards, GNUstep compliance to
@cindex standards compliance
@cindex OpenStep compliance
@cindex OS X compatibility

GNUstep is generally compatible with the OpenStep specification and with
recent developments of the MacOS-X (Cocoa) API. Where MacOS deviates from the
OpenStep API, GNUstep generally attempts to support both versions. In some
cases the newer MacOS APIs are incompatible with OpenStep, and GNUstep usually
supports the richer version.

In order to deal with compatiblity issues, GNUstep uses two mechanisms - it
provides conditionally compiled sections of the library header files, so that
software can be built that will conform strictly to a particular API, and it
provides user default settings to control the behavior of the library at
runtime.

@section Conditional Compilation
@cindex compilation, conditional

Adding an option to a makefile to define one of the following preprocessor
constants will modify the API visible to software being compiled -

@deffn preprocessor NO_GNUSTEP
    GNUstep specific extensions to the OpenStep and MacOS cocoa APIs are
    excluded from the headers. 
@end deffn

@deffn preprocessor STRICT_MACOS_X
    Only methods and classes that are part of the MacOS cocoa API are made
available in the headers.
@end deffn

@deffn preprocessor STRICT_OPENSTEP
    Only methods and classes that are part of the OpenStep specification are
made available in the headers.
@end deffn

Note, these preprocessor constants are used in developer code (ie the code
that users of GNUstep write) rather than by the GNUstep software itself. They
permit a developer to ensure that he/she does not write code which depends
upon API not present on other implementations (in practice, MacOS-X or some
old OPENSTEP systems).  The actual GNUstep libraries are always built with the
full GNUstep API in place, so that the feature set is as consistent as
possible.


@section User Defaults
@cindex user defaults, API compliance

User defaults may be specified ...

@deffn defaults GNU-Debug
An array of strings that lists debug levels to be used within the
program. These debug levels are merged with any which were set on the command
line or added programmatically to the set given by the
[NSProcessInfo-debugSet] method.
@end deffn

@deffn defaults GSLogSyslog
Setting the user default GSLogSyslog to YES will cause log/debug output to be
sent to the syslog facility (on systems which support it), rather than to the
standard error stream. This is useful in environments where stderr has been
re-used strangely for some reason.
@end deffn

@deffn defaults GSMacOSXCompatible
Setting the user default GSMacOSXCompatible to YES will cause MacOS compatible
behavior to be the default at runtime. This default may however be overridden
to provide more fine grained control of system behavior.
@end deffn

@deffn defaults GSOldStyleGeometry
Specifies whether the functions for producing strings describing geometric
structures (NSStringFromPoint(), NSStringFromSize(), and NSStringFromRect())
should produce strings conforming to the OpenStep specification or to MacOS-X
behavior. The functions for parsing those strings should cope with both cases
anyway.
@end deffn

@deffn defaults GSSOCKS
May be used to specify a default SOCKS5 server (and optionally a port
separated from the server by a colon) to which tcp/ip connections made using
the NSFileHandle extension methods should be directed.

This default overrides the SOCKS5_SERVER and SOCKS_SERVER environment variables.
@end deffn

@deffn defaults {Local Time Zone}
Used to specify the name of the timezone to be used by the NSTimeZone class.
@end deffn

@deffn defaults NSWriteOldStylePropertyLists
Specifies whether text property-list output should be in the default MacOS-X
format (XML), or in the more human readable (but less powerful) original
OpenStep format.

Reading of property lists is supported in either format, but only if GNUstep
is built with the libxml library (which is needed to handle XML parsing).

NB. MacOS-X generates illegal XML for some strings - those which contain
characters not legal in XML. GNUstep always generates legal XML, at the cost
of a certain degree of compatibility. GNUstep XML property lists use a
backslash to escape illegal chatracters, and consequently any string
containing either a backslash or an illegal character will be written
differently to the same string on MacOS-X.
@end deffn

@deffn defaults NSLanguages
An array of strings that lists the users prefered languages, in order or
preference. If not found the default is just English.
@end deffn