In The Unicode Standard, Bopomofo implementation is discussed in  Chapter 18 East Asia.

Bopomofo was first encoded in The Unicode Standard version 1.0. The script is now encoded in the following blocks:

BlocksCharacter RangeAdded in Unicode VersionDocumentation
Bopomofo 3100..312F 1.0  U3100.pdf
Bopomofo Extended 31A0..31BF 3.0  U31A0.pdf
Spacing Modifier Letters 02EA..02EB 1.0  U02B0.pdf

Subsequent to version 1.1, the following characters have been added to Bopomofo:

CharactersUnicode VersionDocumentation
312D 5.1  n3179.pdf,  L2/06-338
312E 10.0  L2/15-265
31A0..31B7 3.0  n1713r.rtf L2/98-090
31B8..31BA 6.0  n3246.pdf,  L2/07-215

Documentation refers to  ISO Working Group and Unicode proposals

A number of proposals for its inclusion were submitted to the Unicode Technical Committee and WG2:

1998-03-19 Proposal to add 24 extended Bopomofo and 2 modifier letters for Minnan and Hakka languages in ISO/IEC 10646-1 — TCA ( WG2 N1713.rtf, L2/98-090)

2006-10-19 Proposal to encode one Bopomofo character in the UCS — Michael Everson (Yè Mìháo), H. W. Ho, Andrew West (Wèi An) ( WG2 N3179,  L2/06-338)

2007-04-20 Proposal to encode two Bopomofo characters in UCS — TCA ( WG2 N3246,  L2/07-215)

2009-01-25 Proposal to encode three Bopomofo letters for Hmu and Ge — Andrew West ( WG2 N3570,  L2/09-049)

2014-08-01 BOPOMOFO LETTER I — Taiwan MOE / Ken Lunde ( WG2 N4609,  L2/14-189)

2016-04-21 Proposal to encode one Bopomofo letter — Andrew West (WG2 N4717,  L2/16-106)

UTC #147 Minutes ( L2/16-121) (See C.16 for decision and action items)