# user_caps 5

    user_caps(5)                                                      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.

           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.

              U8 boolean,  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
                 terminfo(5).

                 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(1), infocmp(1).

## AUTHORS

           Thomas E. Dickey
           beginning with ncurses 5.0 (1999)

                                                                      user_caps(5)