Text Tables

Contents

Description

Files with names of the form *.ttb are text tables, and with names of the form *.tti are text subtables. They are used by BRLTTY to translate the characters on the screen into their corresponding 8-dot computer braille representations (see Braille Dots for details).

Text tables can usually be found in the /etc/brltty/Text/ directory (see Local Customization for more details). See Text Table List for a list of BRLTTY's text tables.

A text table consists of a sequence of directives, one per line, which define how each character is to be represented in braille. UTF-8 character encoding must be used. Whitespace (blanks, tabs) at the beginning of a line, as well as before and/or after any operand of any directive, is ignored. Lines containing only whitespace are ignored. If the first non-whitespace character of a line is # then that line is a comment and is ignored.

The precedence for determining the braille representation for a character is as follows:

  1. If the character is within the Unicode braille Row (U+2800 through U+28FF) then its low-order eight bits are used as follows:

    Hex

    Binary

    Dot

    01

    00000001

    1

    02

    00000010

    2

    04

    00000100

    3

    08

    00001000

    4

    10

    00010000

    5

    20

    00100000

    6

    40

    01000000

    7

    80

    10000000

    8

  2. If the character is within the Unicode private use row U+F000 through U+F0FF then its low-order byte is:

    1. interpreted as a single-byte character within the locAL character set
    2. translated to Unicode
    3. reprocessed
  3. An explicit representation (defined via The Char Directive, The Glyph Directive, or The Byte Directive.

  4. An equivalent representation (defined via The Alias Directive).

  5. The explicit representation of the Unicode base character.

  6. The explicit representation of the transliterated ASCII character.

  7. The explicit representation of the Unicode Replacement Character (U+FFFD).

  8. The explicit representation of a question mark (?).

  9. All eight braille dots.

Directives

The Char Directive

char character dots # comment

Use this directive to specify how a Unicode character is to be represented in braille. Characters defined via this directive can also be entered from a braille keyboard. If several characters have the same braille representation then only one of them should be defined via this directive - the others should be defined via The Glyph Directive (which has the same syntax). If more than one character with the same braille representation is defined via this directive (which is allowed for backward compatibility) then the first one is used when entered from a braille keyboard.

character
The character being defined (see The String Operand for details).
dots
The braille representation for the character being defined (see The Dots Operand for details).

Examples:

char a 1
char b (12)
char c ( 4  1   )
char \\ 12567
char \s 0
char \x20 ()
char \<LATIN_SMALL_LETTER_D> 145

The Glyph Directive

glyph character dots # comment

Use this directive to specify how a Unicode character is to be represented in braille. Characters defined via this directive are output-only - they cannot be entered from a braille keyboard.

See The Char Directive for syntax, examples, etc.

The Alias Directive

alias from to # comment

Use this directive to define the from Unicode character such that it has the same braille representation as the to Unicode character. See The String Operand for details on how to specify both operands.

The Byte Directive

byte byte dots # comment

Use this directive to specify how a character in the local character set is to be represented in braille. It has been retained for backward compatibility but should not be used. Unicode characters should be defined (via either The Char Directive or The Glyph Directive) so that the text table remains valid regardless of what the local character set is.

byte
The character being defined. It may be specified in any of the ways supported by The String Operand except that the Unicode-specific forms (\u, \U, \<) may not be used.
dots
The braille representation for the character being defined (see The Dots Operand for details).

The Include Directive

include file # comment

Use this directive to include the content of another file. It is recursive, which means that an included file can itself include yet another file. Care must be taken to ensure that an "include loop" is not created.

file
The file to be included. It may be either a relative or an absolute path. If relative, it is anchored at the directory containing the including file.

The Assign Directive

assign variable value

Use this directive to create or update a variable associated with the current nesting level (see The BeginVariables Directive) of the current include level (see The Include Directive). The variable is visible to the current and to lower include levels, but not to higher include levels.

variable
The name of the variable. If the variable doesn't already exist at the current include level then it is created.
value
The value that is to be assigned to the variable. If it's not supplied then a zero-length (null) value is assigned.

Examples:

assign nullValue
assign shortValue word
assign longValue a\svalue\swith\sspaces
assign IndirectValue \{variableName}

The AssignDefault Directive

assignDefault variable value

Use this directive to assign a default value to a variable associated with the current nesting level (see The BeginVariables Directive) of the current include level (see The Include Directive). It's functionally equivalent to:

ifNotVar variable assign variable value

See The Assign Directive and The IfNotVar Directive for more details.

variable
The name of the variable. If the variable doesn't already exist at the current include level then it is created. If it does already exist then it is not modified.
value
The value that is to be assigned to the variable if it doesn't already exist. If it's not supplied then a zero-length (null) value is assigned.

Examples:

assignDefault format plain\stext

The IfVar Directive

ifVar variable directive

Use this directive to only process one or more directives if a variable exists.

variable
The name of the variable whose existence is to be tested.
directive
The directive that is to be conditionally processed. It may contain spaces. This operand is optional. If it isn't supplied then this directive applies to all subsequent lines until The EndIf Directive or The Else Directive that is at the same conditional nesting level.

Examples:

ifVar var1 ifVar var2 assign concatenation \{var1}\{var2}

The IfNotVar Directive

ifNotVar variable directive

Use this directive to only process one or more directives if a variable doesn't exist.

variable
The name of the variable whose existence is to be tested.
directive
The directive that is to be conditionally processed. It may contain spaces. This operand is optional. If it isn't supplied then this directive applies to all subsequent lines until The EndIf Directive or The Else Directive that is at the same conditional nesting level.

Examples:

ifNotVar var1 assign var1 default\svalue

The BeginVariables Directive

beginVariables

Use this directive to open a new variable nesting level. The Assign Directive) will define variables at this new nesting level, and will hide variables with the same names in any previous nesting level. These variables will remain defined until The EndVariables Directive that is at the same variable nesting level.

Examples:

assign x 1
# \{x} evaluates to 1
beginVariables
# \{x} still evaluates to 1
assign x 2
# \{x} now evaluates to 2
endVariables
# \{x} evaluates to 1 again

The EndVariables Directive

endVariables

Use this directive to close the current variable nesting level. See The BeginVariables Directive for details.

The ListVariables Directive

listVariables

Use this directive to list all of the currently defiined variables. It can be helpful when debugging.

The EndIf Directive

endIf

Use this directive to terminate the current conditional nesting level.

Examples:

ifVar x
   These lines will be processed if a variable named x exists.
endIf

The Else Directive

else

Use this directive to negate the test associated with the current conditional nesting level.

Examples:

assign x some\svalue
ifVar x
   These lines will be processed.
else
   These lines won't be processed.
endIf

Operands

The String Operand

A string operand may be specified as a non-whitespace sequence of:

  • Any single character other than a backslash (\\) or a white-space character.

  • A backslash-prefixed special character. These are:

    Sequence

    Meaning

    \b

    The backspace character.

    \f

    The formfeed character.

    \n

    The newline character.

    \o###

    The three-digit octal representation of a character.

    \r

    The carriage return character.

    \s

    The space character.

    \t

    The horizontal tab character.

    \u####

    The four-digit hexadecimal representation of a character.

    \U########

    The eight-digit hexadecimal representation of a character.

    \v

    The vertical tab character.

    \x##

    The two-digit hexadecimal representation of a character.

    \X##

    (the case of the X and of the digits isn't significant)

    \<name>

    The Unicode name of a character (use _ for space).

    \{variable}

    The value of a variable.

    \\

    A literal backslash.

    \#

    A literal number sign.

The Dots Operand

A dots operand is a sequence of one to eight dot numbers. If the dot numbers are enclosed within (parentheses) then they may be separated from one another by whitespace. A dot number is a digit within the range 1-8 as defined by the standard braille dot numbering convention (see Braille Dots for details). The special dot number 0 is recognized when not enclosed within (parentheses), and means no dots - it may not be used in conjunction with any other dot number.

Text Table List

Name Description
auto locale-based autoselection
ar Arabic (generic)
as Assamese
awa Awadhi
bg Bulgarian
bh Bihari
bn Bengali
bo Tibetan
bra Braj
brf Braille Ready Format (for viewing .brf files within an editor or pager)
cs Czech
cy Welsh
da Danish
de German
dra Dravidian
el Greek
en English
en_CA English (Canada)
en_GB English (United Kingdom)
en_US English (United States)
eo Esperanto
es Spanish
et Estonian
fi Finnish
fr French
fr_CA French (Canada)
fr_FR French (France)
ga Irish
gd Gaelic
gon Gondi
gu Gujarati
he Hebrew
hi Hindi
hr Croatian
hu Hungarian
hy Armenian
is Icelandic
it Italian
kha Khasi
kn Kannada
kok Konkani
kru Kurukh
lt Lituanian
lv Latvian
mg Malagasy
mi Maori
ml Malayalam
mni Manipuri
mr Marathi
mt Maltese
mun Munda
mwr Marwari
ne Nepali
new Newari
nl Dutch
nl_BE Dutch (Belgium)
nl_NL Dutch (Netherlands)
no Norwegian
nwc Newari (old)
or Oriya
pa Panjabi
pi Pali
pl Polish
pt Portuguese
ro Romanian
ru Russian
sa Sanskrit
sat Santali
sd Sindhi
sk Slovak
sl Slovenian
sv Swedish
sw Swahili
ta Tamil
te Telugu
tr Turkish
vi Vietnamese