- You must also define <STRONG>_XOPEN_SOURCE_EXTENDED</STRONG> when compiling for the
- wide-character library to use the extended (wide-character) func-
- tions. The <STRONG>curses.h</STRONG> file which is installed for the wide-charac-
- ter library is designed to be compatible with the normal library's
+ <STRONG>o</STRONG> Originally, the wide-character feature required the symbol
+ <STRONG>_XOPEN_SOURCE_EXTENDED</STRONG> but that was only valid for XPG4
+ (1996).
+
+ <STRONG>o</STRONG> Later, that was deemed conflicting with <STRONG>_XOPEN_SOURCE</STRONG> defined
+ to 500.
+
+ <STRONG>o</STRONG> As of mid-2018, none of the features in this implementation
+ require a <STRONG>_XOPEN_SOURCE</STRONG> feature greater than 600. However,
+ X/Open Curses, Issue 7 (2009) recommends defining it to 700.
+
+ <STRONG>o</STRONG> Alternatively, you can enable the feature by defining
+ <STRONG>NCURSES_WIDECHAR</STRONG> with the caveat that some other header file
+ than <STRONG>curses.h</STRONG> may require a specific value for <STRONG>_XOPEN_SOURCE</STRONG>
+ (or a system-specific symbol).
+
+ The <STRONG>curses.h</STRONG> file which is installed for the wide-character
+ library is designed to be compatible with the normal library's