+ <B>o</B> SVr4 provided <B>traceon</B> and <B>traceoff</B>, to control whether debugging
+ information was written to the "trace" file. While the functions
+ were always available, this feature was only enabled if <B>DEBUG</B> was
+ defined when building the library.
+
+ The SVr4 tracing feature is undocumented.
+
+ <B>o</B> PDCurses provides <B>traceon</B> and <B>traceoff</B>, which (like SVr4) are al-
+ ways available, and enable tracing to the "trace" file only when a
+ debug-library is built.
+
+ PDCurses has a short description of these functions, with a note
+ that they are not present in X/Open Curses, ncurses or NetBSD. It
+ does not mention SVr4, but the functions' inclusion in a header
+ file section labeled "Quasi-standard" hints at the origin.
+
+ <B>o</B> NetBSD does not provide functions for enabling/disabling traces.
+ It uses environment variables <B>CURSES_TRACE_MASK</B> and <B>CURS-</B>
+ <B>ES_TRACE_FILE</B> to determine what is traced, and where the results
+ are written. This is available only when a debug-library is built.
+
+ The NetBSD tracing feature is undocumented.
+
+ A few ncurses functions are not provided when symbol versioning is
+ used: