+.PP
+This implementation of \fBtput\fP differs from AT&T \fBtput\fP in
+two important areas:
+.bP
+\fB@TPUT@\fP \fIcapname\fP writes to the standard output.
+That need not be a regular terminal.
+However, the subcommands which manipulate terminal modes
+may not use the standard output.
+.IP
+The AT&T implementation's \fBinit\fP and \fBreset\fP commands
+use the BSD (4.1c) \fBtset\fP source, which manipulates terminal modes.
+It successively tries standard output, standard error, standard input
+before falling back to \*(lq/dev/tty\*(rq and finally just assumes
+a 1200Bd terminal.
+When updating terminal modes, it ignores errors.
+.IP
+Until changes made after ncurses 6.0, \fB@TPUT@\fP did not modify terminal modes.
+\fB@TPUT@\fP now uses a similar scheme,
+using functions shared with \fB@TSET@\fP
+(and ultimately based on the 4.4BSD \fBtset\fP).
+If it is not able to open a terminal, e.g., when running in \fBcron\fP,
+\fB@TPUT@\fP will return an error.
+.bP
+AT&T \fBtput\fP guesses the type of its \fIcapname\fP operands by seeing if
+all of the characters are numeric, or not.
+.IP
+Most implementations which provide support for \fIcapname\fR operands
+use the \fItparm\fP function to expand parameters in it.
+That function expects a mixture of numeric and string parameters,
+requiring \fB@TPUT@\fP to know which type to use.
+.IP
+This implementation uses a table to determine the parameter types for
+the standard \fIcapname\fR operands, and an internal library
+function to analyze nonstandard \fIcapname\fR operands.
+.PP
+The \fBlongname\fR and \fB\-S\fR options, and the parameter-substitution
+features used in the \fBcup\fR example,
+were not supported in BSD curses before 4.3reno (1989) or in
+AT&T/USL curses before SVr4 (1988).
+.PP
+IEEE Std 1003.1/The Open Group Base Specifications Issue 7 (POSIX.1-2008)
+documents only the operands for \fBclear\fP, \fBinit\fP and \fBreset\fP.
+There are a few interesting observations to make regarding that:
+.bP
+In this implementation, \fBclear\fP is part of the \fIcapname\fR support.
+The others (\fBinit\fP and \fBlongname\fP) do not correspond to terminal
+capabilities.
+.bP
+Other implementations of \fBtput\fP on
+SVr4-based systems such as Solaris, IRIX64 and HPUX
+as well as others such as AIX and Tru64
+provide support for \fIcapname\fR operands.
+.bP
+A few platforms such as FreeBSD recognize termcap names rather
+than terminfo capability names in their respective \fBtput\fP commands.
+Since 2010, NetBSD's \fBtput\fP uses terminfo names.
+Before that, it (like FreeBSD) recognized termcap names.
+.PP
+Because (apparently) \fIall\fP of the certified Unix systems
+support the full set of capability names, the reasoning for documenting
+only a few may not be apparent.
+.bP
+X/Open Curses Issue 7 documents \fBtput\fP differently, with \fIcapname\fP
+and the other features used in this implementation.
+.bP
+That is, there are two standards for \fBtput\fP: POSIX (a subset) and X/Open Curses (the full implementation).
+POSIX documents a subset to avoid the complication of including X/Open Curses
+and the terminal capabilities database.
+.bP
+While it is certainly possible to write a \fBtput\fP program without using curses,
+none of the systems which have a curses implementation provide
+a \fBtput\fP utility which does not provide the \fIcapname\fP feature.