Text Tables ----------- 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. 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. White-space (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 white-space are ignored. If the first non-white-space character of a line is "#" then that line is a comment and is ignored. =============================================================================== The Char Directive ------------------ char <character> <dots> # <comment> Use the "char" directive to specify how a Unicode character is to be represented in braille. The <character> operand specifies the Unicode character being defined. It may be: * Any single character other than a backslash or a white-space character. * A backslash-prefixed special character. These are: - \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) - \# A literal number sign. - \<name> The Unicode name of a character (use _ for space). - \\ A literal backslash. The <dots> operand specifies the braille representation of the Unicode character. It is a sequence of one to eight dot numbers. If the dot number sequence is enclosed within parentheses then the dot numbers may be separated from one another by white-space. A dot number is a digit within the range 1-8 as defined by the standard braille dot numbering convention (see README-DOTS). 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. 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 Byte Directive ------------------ byte <byte> <dots> # <comment> Use the "byte" 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 the "char" directive) so that the text table remains valid regardless of what the local character set is. The <byte> operand specifies the local character being defined. It may be specified in the same ways as the <character> operand of the "char" directive except that the Unicode-specific forms (\u, \U, \<) may not be used. The <dots> operand specifies the braille representation of the local character. It may be specified in the same ways as the <dots> operand of the "char" directive. =============================================================================== The Include Directive --------------------- include <file> # <comment> Use the "include" directive to include the content of a text subtable. It is recursive, which means that any text subtable can itself include yet another text subtable. Care must be taken to ensure that an "include loop" is not created. The <file> operand specifies 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. ===============================================================================
