# user_caps 5

    user_caps(5)                  File Formats Manual                 user_caps(5)

## NAME

           user_caps - user-defined terminfo capabilities

## SYNOPSIS

           tic -x, infocmp -x

## DESCRIPTION

### Background

           Before  ncurses 5.0, terminfo databases used a fixed repertoire of ter-
           minal 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  ter-
           minfo  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 doc-
               umentation.  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 con-
               figured 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 var-
               ious systems past the documented X/Open Curses features.  For exam-
               ple, 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.  The  box1  capa-
               bility  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 unan-
               ticipated 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, deter-
           mine 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 prede-
           fined 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  applica-
               tion, 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,  con-
               trol,  etc.).   While  terminfo and termcap have a set of 60 prede-
               fined function-key  names,  to  which  a  series  of  keys  can  be
               assigned,  that  is  insufficient for more than a dozen keys multi-
               plied by more than a couple of modifier combinations.  The  ncurses
               database  uses a convention based on xterm to provide extended spe-
               cial-key names.

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

### 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.

              RGB
                 boolean, number or string, 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 char-
                 acter 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 mouse mode.

### Extended key-definitions

           Several terminals provide the ability to send distinct strings for com-
           binations of modified special keys.  There  is  no  standard  for  what
           those keys can send.

           Since 1999, xterm 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  spe-
           cial keys in the terminal description.

           Starting  with  the curses convention that key names begin with "k" and
           that shifted special keys are  an  uppercase  name,  ncurses'  terminal
           database defines these names to which a suffix is added:

                Name   Description
                ---------------------------------------------------------------
                kDC    special form of kdch1 (delete character)
                kDN    special form of kcud1 (cursor down)
                kEND   special form of kend (End)
                kHOM   special form of khome (Home)
                kLFT   special form of kcub1 (cursor-left or cursor-back)
                kNXT   special form of knext (Next, or Page-Down)
                kPRV   special form of kprev (Prev, or Page-Up)
                kRIT   special form of kcuf1 (cursor-right, or cursor-forward)
                kUP    special form of kcuu1 (cursor-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 val-
               ues, 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 Net-
           BSD curses.  That implementation stores user-defined capabilities,  but
           makes no use of these capabilities itself.

## SEE ALSO

           tic(1m), infocmp(1m).

## AUTHORS

           Thomas E. Dickey
           beginning with ncurses 5.0 (1999)

                                                                      user_caps(5)