+.PP
+X/Open Curses documents \fBunctrl\fP as declared in \fB<unctrl.h>\fP,
+which \fBncurses\fP does.
+However, \fBncurses\fP' \fB<curses.h>\fP includes \fB<unctrl.h>\fP,
+matching the behavior of SVr4 curses.
+Other implementations may not do that.
+.SS use_env/use_tioctl
+.PP
+If \fBncurses\fP is configured to provide the sp-functions extension,
+the state of \fBuse_env\fP and \fBuse_tioctl\fP may be updated before
+creating each \fIscreen\fP rather than once only
+(\fBcurs_sp_funcs\fR(3X)).
+This feature of \fBuse_env\fP
+is not provided by other implementation of curses.