In The Unicode Standard, Braille Patterns implementation is discussed in  Chapter 21 Notational Systems: Shorthands, Braille, Musical Symbols.

Braille Patterns were encoded in The Unicode Standard version 3.0. It is encoded in the following block:

BlocksCharacter RangeAdded in Unicode VersionDocumentation
Braille Patterns 2800..28FF 3.0  U2800.pdf

A number of proposals for its inclusion were submitted to the Unicode Technical Committee and WG2 (most of the documents leading to the encoding of Braille do not appear to be online):

1998-03-23 Part 1:Architecture and Basic Multilingual Plane AMENDMENT 16: Braille Patterns — WG2 ( WG2 N1770)

2003-09-20 Comments on proposed general category change for Braille symbols — Jack Maartman ( L2/03-335)