# user_caps 5 2025-03-22 ncurses 6.5 File formats

    user_caps(5)                     File formats                     user_caps(5)

## NAME

           user_caps - user-defined terminfo capability format

## SYNOPSIS

           infocmp -x

           tic -x

## DESCRIPTION

### Background

           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 X/Open
           Curses starting 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
               capabilities.

               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:

                   memory_lock
                        (meml) lock memory above cursor

                   memory_unlock
                        (memu) unlock memory

                   box_chars_1
                        (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
               terminfo.

### 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
                 terminal.

                 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.

              RGB
                 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:

                 Boolean
                    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.

                 number
                    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.

                 string
                    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
                 descriptions.

                 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%;,
                           xm=\E[M
                              %?%p4%t%p3%e%{3}%;%' '%+%c
                              %p2%'!'%+%c
                              %p1%'!'%+%c,

                   xterm+sm+1006|xterm SGR-mouse,
                           kmous=\E[<, XM=\E[?1006;1000%?%p1%{1}%=%th%el%;,
                           xm=\E[<%i%p3%d;
                              %p1%d;
                              %p2%d;
                              %?%p4%tM%em%;,

### 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).

## PORTABILITY

           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.

## AUTHORS

           Thomas E. Dickey
           beginning with ncurses 5.0 (1999)

## SEE ALSO

           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                       2025-03-22                      user_caps(5)