Attributes Tables
-----------------

Files with names of the form *.atb are attributes tables, and with names of the 
form *.ati are attributes subtables. They are used when BRLTTY is displaying 
screen attributes rather than screen content. Each of the eight braille dots 
represents one of the eight VGA attribute bits.

An attributes table consists of a sequence of directives, one per line, which 
define how combinations of VGA attributes are 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.

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The Dot Directive
-----------------

   dot <dot> <state> # <comment>

Use the "dot" directive to specify what a specific dot represents. The default 
is that all dots are down and not used to represent anything.

The <dot> operand specifies the dot being defined. It is a single digit within 
the range 1-8 as defined by the standard braille dot numbering convention (see 
README-DOTS).

The <state> operand specifies what the dot represents. It may be:
*  =attribute  The dot is raised if the named attribute is on.
*  ~attribute  The dot is raised if the named attribute is off.

The names of the attribute bits are:
*  0X01  fg-blue
*  0X02  fg-green
*  0X04  fg-red
*  0X08  fg-bright
*  0X10  bg-blue
*  0X20  bg-green
*  0X40  bg-red
*  0X80  blink

Examples:

   dot 1 =fg-red
   dot 2 ~bg-blue

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The Include Directive
---------------------

   include <file> # <comment>

Use the "include" directive to include the content of an attributes subtable. 
It is recursive, which means that any attributes subtable can itself include 
yet another attributes 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.

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