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       user_caps - user-defined terminfo capability format


       infocmp -x

       tic -x


       Before ncurses 5.0, terminfo databases used a fixed repertoire of
       terminal capabilities designed for the SVr2 terminal database in 1984,
       and extended in stages through SVr4 (1989), and standardized in the
       Single Unix Specification beginning in 1995.

       Most of the extensions in this fixed repertoire were additions to the
       tables of Boolean, numeric and string capabilities.  Rather than change
       the meaning of an existing capability, a new name was added.  The
       terminfo database uses a binary format; binary compatibility was
       ensured by using a header which gave the number of items in the tables
       for each type of capability.  The standardization was incomplete:

       o   The binary format itself is not described in the X/Open Curses
           documentation.  Only the source format is described.

           Library developers rely upon the SVr4 documentation, and reverse-
           engineering the compiled terminfo files to match the binary format.

       o   Lacking a standard for the binary format, most implementations copy
           the SVr2 binary format, which uses 16-bit signed integers, and is
           limited to 4096-byte entries.

           The format cannot represent very large numeric capabilities, nor
           can it represent large numbers of special keyboard definitions.

       o   The tables of capability names differ between implementations.

           Although they may provide all of the standard capability names, the
           position in the tables differs because some features were added as
           needed, while others were added (out of order) to comply with
           X/Open Curses.

           While ncurses' repertoire of predefined capabilities is closest to
           Solaris, Solaris's terminfo database has a few differences from the
           list published by X/Open Curses.  For example, ncurses can be
           configured with tables which match the terminal databases for AIX,
           HP-UX or OSF/1, rather than the default Solaris-like configuration.

       o   In SVr4 curses and ncurses, the terminal database is defined at
           compile-time using a text file which lists the different terminal

           In principle, the text-file can be extended, but doing this
           requires recompiling and reinstalling the library.  The text-file
           used in ncurses for terminal capabilities includes details for
           various systems past the documented X/Open Curses features.  For
           example, ncurses supports these capabilities in each configuration:

                    (meml) lock memory above cursor

                    (memu) unlock memory

                    (box1) box characters primary set

           The memory lock/unlock capabilities were included because they were
           used in the X11R6 terminal description for xterm(1).  The box1
           capability is used in tic to help with terminal descriptions
           written for AIX.

       During the 1990s, some users were reluctant to use terminfo in spite of
       its performance advantages over termcap:

       o   The fixed repertoire prevented users from adding features for
           unanticipated terminal improvements (or required them to reuse
           existing capabilities as a workaround).

       o   The limitation to 16-bit signed integers was also mentioned.
           Because termcap stores everything as a string, it could represent
           larger numbers.

       Although termcap's extensibility was rarely used (it was never the
       speaker who had actually used the feature), the criticism had a point.
       ncurses 5.0 provided a way to detect nonstandard capabilities,
       determine their type and optionally store and retrieve them in a way
       which did not interfere with other applications.  These are referred to
       as user-defined capabilities because no modifications to the toolset's
       predefined capability names are needed.

       The ncurses utilities tic and infocmp have a command-line option "-x"
       to control whether the nonstandard capabilities are stored or
       retrieved.  A library function use_extended_names is provided for the
       same purpose.

       When compiling a terminal database, if "-x" is set, tic will store a
       user-defined capability if the capability name is not one of the
       predefined names.

       Because ncurses provides a termcap library interface, these user-
       defined capabilities may be visible to termcap applications:

       o   The termcap interface (like all implementations of termcap)
           requires that the capability names are 2-characters.

           When the capability is simple enough for use in a termcap
           application, it is provided as a 2-character name.

       o   There are other user-defined capabilities which refer to features
           not usable in termcap, e.g., parameterized strings that use more
           than two parameters or use more than the trivial expression support
           provided by termcap.  For these, the terminfo database should have
           only capability names with 3 or more characters.

       o   Some terminals can send distinct strings for special keys (cursor-,
           keypad- or function-keys) depending on modifier keys (shift,
           control, etc.).  While terminfo and termcap have a set of 60
           predefined function-key names, to which a series of keys can be
           assigned, that is insufficient for more than a dozen keys
           multiplied by more than a couple of modifier combinations.  The
           ncurses database uses a convention based on xterm(1) to provide
           extended special-key names.

           Fitting that into termcap's limitation of 2-character names would
           be pointless.  These extended keys are available only with

   Recognized Capabilities
       The ncurses library uses the user-definable capabilities.  While the
       terminfo database may have other extensions, ncurses makes explicit
       checks for these:

          AX Boolean, asserts that the terminal interprets SGR 39 and SGR 49
             by resetting the foreground and background color, respectively,
             to the default.

             This is a feature recognized by the screen program as well.

          E3 string, tells how to clear the terminal's scrollback buffer.
             When present, the clear(1) program sends this before clearing the

             The command "tput clear" does the same thing.

          NQ Boolean, used to suppress a consistency check in tic for the
             ncurses capabilities in user6 through user9 (u6, u7, u8 and u9)
             which tell how to query the terminal's cursor position and its
             device attributes.

             Boolean, number or string, used to assert that the
             set_a_foreground and set_a_background capabilities correspond to
             direct colors, using an RGB (red/green/blue) convention.  This
             capability allows the color_content function to return
             appropriate values without requiring the application to
             initialize colors using init_color.

             The capability type determines the values which ncurses sees:

                implies that the number of bits for red, green and blue are
                the same.  Using the maximum number of colors, ncurses adds
                two, divides that sum by three, and assigns the result to red,
                green and blue in that order.

                If the number of bits needed for the number of colors is not a
                multiple of three, the blue (and green) components lose in
                comparison to red.

                tells ncurses what result to add to red, green and blue.  If
                ncurses runs out of bits, blue (and green) lose just as in the
                Boolean case.

                explicitly list the number of bits used for red, green and
                blue components as a slash-separated list of decimal integers.

             Because there are several RGB encodings in use, applications
             which make assumptions about the number of bits per color are
             unlikely to work reliably.  As a trivial case, for example, one
             could define RGB#1 to represent the standard eight ANSI colors,
             i.e., one bit per color.

          U8 number, asserts that ncurses must use Unicode values for line-
             drawing characters, and that it should ignore the alternate
             character set capabilities when the locale uses UTF-8 encoding.
             For more information, see the discussion of NCURSES_NO_UTF8_ACS
             in ncurses(3X).

             Set this capability to a nonzero value to enable it.

          XM string, override ncurses's built-in string which enables/disables
             xterm(1) mouse mode.

             ncurses sends a character sequence to the terminal to initialize
             mouse mode, and when the user clicks the mouse buttons or (in
             certain modes) moves the mouse, handles the characters sent back
             by the terminal to tell it what was done with the mouse.

             The mouse protocol is enabled when the mask passed in the
             mousemask function is nonzero.  By default, ncurses handles the
             responses for the X11 xterm mouse protocol.  It also knows about
             the SGR 1006 xterm mouse protocol, but must to be told to look
             for this specifically.  It will not be able to guess which mode
             is used, because the responses are enough alike that only
             confusion would result.

             The XM capability has a single parameter.  If nonzero, the mouse
             protocol should be enabled.  If zero, the mouse protocol should
             be disabled.  ncurses inspects this capability if it is present,
             to see whether the 1006 protocol is used.  If so, it expects the
             responses to use the SGR 1006 xterm mouse protocol.

             The xterm mouse protocol is used by other terminal emulators.
             The terminal database uses building-blocks for the various xterm
             mouse protocols which can be used in customized terminal

             The terminal database building blocks for this mouse feature also
             have an experimental capability xm.  The "xm" capability
             describes the mouse response.  Currently there is no interpreter
             which would use this information to make the mouse support
             completely data-driven.

             xm shows the format of the mouse responses.  In this experimental
             capability, the parameters are

               p1   y-ordinate

               p2   x-ordinate

               p3   button

               p4   state, e.g., pressed or released

               p5   y-ordinate starting region

               p6   x-ordinate starting region

               p7   y-ordinate ending region

               p8   x-ordinate ending region

             Here are examples from the terminal database for the most
             commonly used xterm mouse protocols:

               xterm+x11mouse|X11 xterm mouse protocol,
                       kmous=\E[M, XM=\E[?1000%?%p1%{1}%=%th%el%;,
                          %?%p4%t%p3%e%{3}%;%' '%+%c

               xterm+sm+1006|xterm SGR-mouse,
                       kmous=\E[<, XM=\E[?1006;1000%?%p1%{1}%=%th%el%;,

   Extended Key Definitions
       Several terminals provide the ability to send distinct strings for
       combinations of modified special keys.  There is no standard for what
       those keys can send.

       Since 1999, xterm(1) has supported shift, control, alt, and meta
       modifiers which produce distinct special-key strings.  In a terminal
       description, ncurses has no special knowledge of the modifiers used.
       Applications can use the naming convention established for xterm to
       find these special keys in the terminal description.

       Starting with the curses convention that capability codes describing
       the input generated by a terminal's key caps begin with "k", and that
       shifted special keys use uppercase letters in their names, ncurses's
       terminal database defines the following names and codes to which a
       suffix is added.

            Code   Description
            kDC    shifted kdch1 (delete character)
            kDN    shifted kcud1 (cursor down)
            kEND   shifted kend (end)
            kHOM   shifted khome (home)
            kLFT   shifted kcub1 (cursor back)
            kNXT   shifted knext (next)
            kPRV   shifted kprev (previous)
            kRIT   shifted kcuf1 (cursor forward)
            kUP    shifted kcuu1 (cursor up)

       Keycap nomenclature on the Unix systems for which curses was developed
       differs from today's ubiquitous descendants of the IBM PC/AT keyboard
       layout.  In the foregoing, interpret "backward" as "left", "forward" as
       "right", "next" as "page down", and "prev(ious)" as "page up".

       These are the suffixes used to denote the modifiers:

            Value   Description
            2       Shift
            3       Alt
            4       Shift + Alt
            5       Control
            6       Shift + Control
            7       Alt + Control
            8       Shift + Alt + Control
            9       Meta
            10      Meta + Shift
            11      Meta + Alt
            12      Meta + Alt + Shift
            13      Meta + Ctrl
            14      Meta + Ctrl + Shift
            15      Meta + Ctrl + Alt
            16      Meta + Ctrl + Alt + Shift

       None of these are predefined; terminal descriptions can refer to names
       which ncurses will allocate at runtime to key-codes.  To use these keys
       in an ncurses program, an application could do this:

       o   using a list of extended key names, ask tigetstr(3X) for their
           values, and

       o   given the list of values, ask key_defined(3X) for the key-code
           which would be returned for those keys by wgetch(3X).


       The "-x" extension feature of tic and infocmp has been adopted in
       NetBSD curses.  That implementation stores user-defined capabilities,
       but makes no use of these capabilities itself.


       Thomas E. Dickey
       beginning with ncurses 5.0 (1999)


       infocmp(1M), tic(1M)

       The terminal database section NCURSES USER-DEFINABLE CAPABILITIES
       summarizes commonly-used user-defined capabilities which are used in
       the terminal descriptions.  Some of those features are mentioned in
       screen(1) or tmux(1).

       XTerm Control Sequences provides further information on the xterm(1)
       features that are used in these extended capabilities.

ncurses 6.5                       2024-03-16                      user_caps(5)

ncurses 6.5 - Generated Tue May 7 16:14:38 CDT 2024
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