The Unicode block Braille Patterns (U+2800..U+28FF) contains all 256 possible patterns of an 8-dot braille cell, thereby including the complete 6-dot cell range.^[3] In Unicode, a braille cell does not have a letter or meaning defined. For example, Unicode does not define U+2817 ⠗ to be "R".

Symbols, not letters

In Unicode braille characters are not defined as belonging to any other script, but are defined as the Braille script.^[3] That is, the patterns are available as symbols, without connection to an alphabetic letter or a number. This is because the same symbol can be used in multiple scripts, e.g. as a Latin character, a Vietnamese character, a Chinese character and a digit. For example: although U+2813 ⠓ BRAILLE PATTERN DOTS-125 represents the letter "H" in basic braille, its Unicode definition makes no reference to "H", and it is just as valid representing Korean ᄐ t-, or Japanese り ri.

For this reason – a dot-pattern is not a letter – Unicode declares that, strictly speaking, braille patterns are 'symbols', not 'letters'. The General Property is "So" (Symbol, other), not "Lo" (Letter, other). Beyond that declaration, however, braille is treated as a script in multiple places. E.g., the character property "Script" for the 256 braille code points is ISO 15924 "Brai", for braille. This way, searching users and programs are led to the right place.

Identifying, naming and ordering

Braille dot numbering

Hexadecimal value of braille dots

The coding is in accordance with ISO/TR 11548-1 Communication aids for blind persons.^[3] Unicode uses the standard dot-numbering 1 to 8. Historically only the 6-dot cell was used in braille. The lower two dots were added later, which explains the irregular numbering 1-2-3-7 in the left column and 4-5-6-8 in the right column. Where dots 7 and 8 are not raised, there is no distinction between 6-dot and 8-dot definitions.

The Unicode name of a specific pattern mentions the raised dots: U+2813 ⠓ BRAILLE PATTERN DOTS-125 has dots 1, 2 and 5 raised. By exception, the zero dot raised pattern is named U+2800 ⠀ BRAILLE PATTERN BLANK.^[4]

In the 8-dot cell each dot individually can be raised or not. That creates 2⁸=256 different patterns. By mapping each of the eight dots to a bit in a byte (in a little-endian order), and by defining "0"/"1" for not raised/raised per bit, every specific pattern generates an identifying binary number. So the pattern with dots 1-2-5 raised would yield (00010011)₂, equivalent to (13)₁₆ or (19)₁₀.

The mapping can also be computed by adding together the hexadecimal values, seen at right, of the dots raised. So the pattern with dots 1-2-5 raised would yield 1₁₆+2₁₆+10₁₆ = 13₁₆. Whether computed directly in hexadecimal, or indirectly via binary, the result is added to 2800₁₆, the offset for the Braille Patterns Unicode block.

There is no regular mapping to the braille ASCII numbering.

Other uses

The Braille Pattern characters are commonly^[6] used in terminal applications as a way to draw multiple pixels per character.

History

The following Unicode-related documents record the purpose and process of defining specific characters in the Braille Patterns block:

References