In The Unicode Standard, Khmer script implementation is discussed in  Chapter 16 Southeast Asia.

The Khmer script was encoded in The Unicode Standard version 3.0. Since that time the encoding has undergone a number of modifications; the script is now encoded in the following blocks:

BlocksCharacter RangeAdded in Unicode VersionUnicode Chart
Khmer 1780..17FF 3.0  U1780.pdf
Khmer Symbols 19E0..19FF 4.0  U19E0.pdf

Subsequent to version 3.0, the following characters have been added to the Khmer script:

CharactersUnicode VersionDocumentation
17DD 4.0  n2470.pdf/ L2/02-100
17F0..17F9 4.0  n2470.pdf/ L2/02-100
19E0..19FF 4.0  n2471.pdf/ L2/02-101

Documentation refers to  ISO Working Group and Unicode proposals

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

1992-11-25 Unicode Technical Report #1 — Andy Daniels ( TR1)

1997-01-22 Proposal for encoding the Khmer script in ISO 10646 — Michael Everson ( (Unofficial HTML version of WG2 N1524), L2/97-040 (not online))

1998-03-17 Khmer and Burmese Ad-Hoc Meeting Report — SC2/WG2 ( WG2 N1729, L2/98-101 (not online))

1998-05-05 Part 1:Architecture and Basic Multilingual Plane AMENDMENT 25: Khmer — WG2 ( WG2 N1825khmer)

1999-01-27 Soft Space in Indic scripts — Maurice Bauhahn ( L2/99-037)

2000-01-05 Khmer update (Amendment 25) — T.K. Sato ( WG2 N2149.doc,  L2/00-009)

2000-02-23 10646-Amd.#25 (Khmer) correction request — Sato, WG2 ( WG2 N2164.doc,  L2/00-056)

2000-04-06 Corrections to Khmer character tables in 10646 and Unicode — Michel Suignard ( L2/00-109)

2000-09-19 Working Draft of Tables & Character Names for Editorial correction to Khmer for 10646-1:2000 — Unicode ( WG2 N2274,  L2/00-338)

2001-08-06 Serious bug in Khmer, Myanmar combining classes — Ken Whistler ( L2/01-307)

2001-08-07 More on L2/01-307 – Khmer and Myanmar — Martin Hosken, Ken Whistler ( L2/01-308)

2001-08-14 Khmer issues on the horizon — Rick McGowan, Ken Whistler ( L2/01-310)

2001-10-11 Response to Cambodian official objection to Khmer block (N2380) — Maurice Bauhahn, Michael Everson ( WG2 N2385,  L2/01-382)

2001-10-14 Cambodian official objection to the existing Khmer block in UCS — Cambodia NB ( WG2 N2380,  L2/01-372,  L2/01-421)

2001-10-17 Letter from Cambodia to JTC 1 Chairman Regarding Khmer Character Encoding in ISO/IEC 10646 — Mr. Tom Frost, JTC 1 Chairman ( L2/01-394)

2001-11-04 Response to WG2 Document N2385, 2001-10-11 — Cambodian NB ( WG2 N2406,  L2/01-443)

2001-12-02 Response and Proposal for Khmer Encoding — Paul Nelson ( L2/02-083)

2001-12-19 Ordering rules for Khmer — Kent Karlsson ( L2/01-476)

2002-01-14 Character Properties for avagrahas, etc. — Kenneth Whistler ( L2/02-017)

2002-01-14 Character Properties for repetition marks — Kenneth Whistler ( L2/02-016)

2002-02-08 Cambodian Thoughts — Mark Davis ( L2/02-073)

2002-02-13 Proposal to add Krung voicing marks — Paul Nelson ( WG2 N2472,  L2/02-099)

2002-02-13 Proposal to add Khmer lunar dates — CHEA Sok Huor, LAO Kim Leang, HARADA Shiro, Norbert KLEIN ( WG2 N2471,  L2/02-101)

2002-02-13 Proposal to encode Khmer subscript characters — CHEA Sok Huor, LAO Kim Leang, HARADA Shiro, Norbert KLEIN ( L2/02-096)

2002-02-13 Proposal to deprecate Khmer characters — CHEA Sok Huor, LAO Kim Leang, HARADA Shiro, Norbert KLEIN ( L2/02-097)

2002-02-13 Proposal to add missing Khmer characters — CHEA Sok Huor, LAO Kim Leang, HARADA Shiro, Norbert KLEIN ( WG2 N2470,  L2/02-100)

2002-02-13 Proposal to add Om and Am — CHEA Sok Huor, LAO Kim Leang, HARADA Shiro, Norbert KLEIN ( L2/02-098)

2002-03-31 On the suitability of the COENG encoding model for Khmer — Michael Everson ( WG2 N2412,  L2/02-131)

2002-05-03 On the unsuitability of the “COENG encoding model” for Khmer — Cambodian Committee for Standardization of Khmer Characters in Computers ( WG2 N2458,  L2/02-196)

2002-05-14 Cambodian stance regarding Khmer code table in Unicode 3.2 — Cambodia ( WG2 N2459,  L2/02-211)

2003-11-10 Problem with Khmer / ZWJ / ZWNJ — Mark Davis ( L2/03-430)

2004-03-09 Ordering rules for Khmer, Thai, and Lao; CTT suggestion — Kent Karlsson ( WG2 N2717.doc,  L2/04-110)

2004-03-09 Ordering rules for Khmer, Thai, and Lao; suggestions for annex C.2 changes and a new annex B.5 — Kent Karlsson ( WG2 N2718.doc,  L2/04-111)

2005-10-26 TR 29 and Myanmar/Khmer — Martin Hosken ( L2/05-352)

2006-07-27 Re: document Sk vs Lm — Martin Hosken ( L2/06-243)

2008-03-02 Criteria for the encoding of script-specific dandas — Unicode and US National Body ( WG2 N3457,  L2/08-118)

2014-02-05 A bag of suggested improvements to Unicode’s provisional Indic properties — Roozbeh Pournader, Behdad Esfahbod ( L2/14-065)

2014-05-08 Improvements requested for Unicode Indic properties (two text file appendices are included) — Roozbeh Pournader ( L2/14-126)

2016-05-12 Additions to Indic Syllabic Category for Myanmar and Khmer — Roozbeh Pournader ( L2/16-163)