In The Unicode Standard, Combining marks implementation is discussed in  Chapter 7 Europe-I: Modern and Liturgical Scripts. In general, combining marks inherit script properties from the script being used. They are used in Latin, Cyrillic, Greek and have even been used in Tifinagh, Coptic, Newa and Caucasian Albanian. Other scripts, such as Arabic or most of the Indic scripts, have combining marks which are specific to that script.

The Combining marks were first encoded in The Unicode Standard version 1.0. Since that time a number of other combining marks have been encoded. Combining marks are now encoded in the following blocks:

BlocksCharacter RangeAdded in Unicode VersionDocumentation
Combining Diacritical Marks 0300..036F 1.0  U0300.pdf
Combining Diacritical Marks Supplement 1DC0..1DFF 4.1  U1DC0.pdf
Combining Diacritical Marks for Symbols 20D0..20FF 1.0  U20D0.pdf
Combining Half Marks FE20..FE2F 1.1  UFE20.pdf

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

CharactersUnicode VersionDocumentation
0346..034E 3.0  n1845.pdf L2/98-299
034F 3.2  n2236.htm L2/00-274
0350..0357 4.0  n3027.pdf L2/06-027 and  n2713.pdf L2/04-107
0358 4.1  n2713.pdf L2/04-107
0359 4.1  n2612-4.pdf L2/03-186
035A 4.1  n2524.pdf L2/02-203R2 and  n2630.pdf L2/02-364
035B 4.1  n2597.pdf L2/03-219
035C 4.1  n2594.pdf L2/03-142R
035D..035F 4.0  n2457.pdf L2/02-204
0362 3.0  n1845.pdf L2/98-299
0363..036F 3.2  n2266.pdf L2/00-330
1DC0..1DC1 4.1  n2642.pdf L2/03-324
1DC2 4.1  n2740.pdf L2/04-047 and  n2763r.pdf L2/04-171
1DC3 4.1  n2763r.pdf L2/04-171
1DC4..1DCA 5.0  n2906.pdf L2/04-246R
1DCB..1DCC 5.1  n3048.pdf L2/06-214
1DCD..1DE6 5.1  n3027.pdf L2/06-027
1DF6..1DF9 10.0  
1DFB 9.0  L2/14-285
1DFC 6.0  n3571.pdf L2/09-028
1DFD 5.2  n3447.pdf L2/07-334R
1DFE..1DFF 5.0  n2989.pdf L2/05-261
20E2..20E3 3.0  n1668.doc L2/97-206
20E4 3.2  n1941.pdf L2/98-056
20E5..20E8 3.2  n2191.pdf L2/00-094
20E9..20EA 3.2  n2336.pdf L2/01-067
20EB 4.1  n2590.pdf L2/03-194
20EC..20EF 5.0  n2874.pdf L2/04-410
20F0 5.1  n3198.pdf L2/07-108
FE24..FE26 5.1  n3222.pdf L2/07-085R

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:

1998-02-23 Triangular Overlay Character — Rick McGowan, Geoffrey Sampson ( L2/98-056)

1998-12-07 Request for addition of Triangular Overlay Character — Rick McGowan on behalf of UTC ( WG2 N1941,  L2/99-021)

2000-08-09 Proposal for addition of COMBINING GRAPHEME JOINER — Mark Davis on behalf of UTC ( WG2 N2236.htm,  L2/00-274)

2000-09-14 Diacritics for medieval studies — Marc Wilhelm Küster, Isabel Wojtovicz ( WG2 N2266,  L2/00-330)

2001-04-19 General Category for Combining Grapheme Joiner — Mark Davis ( L2/02-148)

2002-03-07 E-mail Response to L2/02-148 (UTC Agenda item: How to make "oo" with combining breve/macron over pair?) — Ken Whistler ( L2/02-176)

2002-03-11 Draft of Proposal to add Latin characters required by Latinized Taiwanese Holo language to ISO/IEC 10646 — Department of Language Education of National Taitung Teachers ( WG2 N2507,  L2/02-348)

2002-05-10 Additional Double Diacritics — US National Body ( WG2 N2457,  L2/02-204)

2002-09-05 Double Combining Stroke — Mark Davis ( L2/02-361)

2002-10-08 Proposal to add one combining diacritic to the UCS — Andrew Glass, Stefan Baums, Richard Salomon ( WG2 N2630,  L2/02-364)

2002-10-30 Double Combining Breve Below, Double Combining Macron — Peter Constable ( L2/02-367)

2003-04-01 Proposal to encode two COMBINING HEART characters in the UCS — Michael Everson, Roozbeh Pournader, John Cowan (WG2 N258A, —  L2/03-121)

2003-06-11 Proposal to encode one additional combining diacritic in the UCS — Maria Pantelia / TLG ( WG2 N2612-4,  L2/03-186)

2003-06-25 Proposal to encode one combining character in the UCS — Lithuanian Standards Board (LST) ( WG2 N2597,  L2/03-219)

2003-07-01 Proposal to encode combining double breve below — Rick McGowan, Peter Constable, Ken Whistler, and Unicode Technical Committee ( WG2 N2594,  L2/03-142)

2003-08-23 Additional Mathematical and Letterlike Characters — UTC( WG2 N2590)

2003-09-27 Proposal on IPA Extensions & Combining Diacritical Marks for ISO/IEC 10646 in BMP — China N.B. ( WG2 N2626,  L2/03-317)

2003-09-29 Proposal to add Combining Right Dot Above as required by Taiwanese Holo language Romanization to ISO/IEC 10646 — TCA ( WG2 N2628,  L2/03-318)

2003-10-06 Proposal to encode additional Greek editorial and punctuation characters in the UCS — Maria Pantelia / TLG ( WG2 N2642,  L2/03-324)

2003-10-20 Comments on “Combining dot above” — China N.B. ( WG2 N2669.doc,  L2/03-369)

2003-10-20 Response to WG2-N2669 — Taiwan NB ( WG2 N2699.doc,  L2/04-076)

2004-03-20 Revised Proposal for encoding A Supplemented Set of IPA Combining Marks, Modifier Letters & Five-Degree Contour Tone Marks in the BMP of the UCS — China N.B. ( WG2 N2713,  L2/04-107)

2004-05-28 Definition of a Code Position for German Umlauts in ISO/IEC 10646 / Unicode — Germany N B ( WG2 N2766,  L2/04-210)

2004-05-29 Proposal to add COMBINING GLAGOLITIC SUSPENSION MARK to the BMP of the UCS — Michael Everson ( WG2 N2763,  L2/04-171)

2004-05-29 Response to WG2-N2713 - Combining right dot above — Taiwan N B ( WG2 N2770,  L2/04-200)

2004-06-02 Romanian Proposal for ISO/IEC 6937 Amendment — Romanian N B ( WG2 N2783,  L2/04-205)

2004-06-07 Using SPACE as a base character — Eric Muller ( L2/04-234)

2004-06-14 Depiction of combining marks in isolation — Gihan Dias ( L2/04-247)

2004-06-20 Response to DIN request regarding umlaut and trema — U S NB ( WG2 N2819,  L2/04-269)

2004-06-21 Proposal to add Invisible Letter to the UCS — Michael Everson, Peter Constable, Rick McGowan, Ken Whistler ( WG2 N2822,  L2/04-268)

2004-07-23 CGJ in German — Mark Davis ( L2/04-304)

2005-08-08 Comments on L2/05-172 (On Criteria for disunifying Diacritics) — P. Andries, F. Yergeau ( L2/05-223)

2005-08-26 Proposal to clarify principles for disunification of combining diacritical marks — Asmus Freytag on behalf of USA (INCTS/L2) and the Unicode Technical Committee ( WG2 N2976,  L2/05-172)

2005-08-27 Response to US/UTC proposal on principles for disunification of combining diacritical marks — Ireland N.B. ( WG2 N2978,  L2/05-240)

2005-09-05 Comments on N2976 (On Criteria for disunifying Diacritics) — P. Andries, F. Yergeau ( WG2 N2981,  L2/05-247)

2006-03-02 Proposal to encode two combining characters in the UCS — Lithuania ( WG2 N3048,  L2/06-214)

2006-07-28 Comments on Capital R Rotunda — Andrew C West ( L2/06-252)

2007-10-22 Proposal to encode two phonetic characters and two Shona characters — Lorna Priest ( WG2 N3447,  L2/07-334)

2008-01-28 Comments on L2/08-049 (WG2 N3382) Egyptological Yod and Cyrillic Breathings — Deborah Anderson, Donald Mastronarde ( L2/08-087)

2008-04-08 Egyptological Yod and Cyrillic breathings — Michael Everson, Bob Richmond ( WG2 N3382,  L2/08-049)

2008-04-08 Position Paper on Egyptological Yod and Cyrillic Breathings — INCITS L2 / UTC ( WG2 N3432,  L2/08-146)

2008-10-25 Proposal to encode a combining diacritical mark for Low German dialect writing — Karl Pentzlin ( L2/08-392)

2009-01-27 Proposal to encode additional characters for the Uralic Phonetic Alphabet — Klaas Ruppel, Tero Aalto, Michael Everson ( WG2 N3571,  L2/09-028)

2009-08-06 COMBINING TRIPLE INVERTED BREVE and other triple-length combining marks — Deborah Anderson ( L2/09-281)

2010-09-23 Preliminary Proposal to enable the use of Combining Triple Diacritics in Plain Text (two possible solutions) — Karl Pentzlin ( WG2 N3915,  L2/10-353)

2010-10-29 Proposal to add characters used in Lithuanian dialectology to the UCS — Vladas Tumasonis, Karl Pentzlin ( WG2 N3914,  L2/10-357)

2011-05-13 Comments on N3914 - Characters for Lithuanian Dialectology — Peter Constable, Ken Whistler ( WG2 N4062,  L2/11-191)

2011-06-08 Proposal to enable the use of Combining Triple Diacritics in Plain Text — Irish NB, German NB ( WG2 N4078,  L2/11-224)

2011-10-15 Proposal to encode combining decimal digits above in the UCS — Martin Schrage, Karl Pentzlin ( WG2 N4212,  L2/11-375)

2011-10-21 Proposal to encode Linguistic Doubt Marks in the UCS — Martin Schrage, Karl Pentzlin ( WG2 N4210,  L2/11-373)

2011-12-15 Letters in support of Lithuanian pre-composed characters — Lithuania, et al ( WG2 N4187,  WG2 N4188,  WG2 N4189,  WG2 N4190,  WG2 N4192,  L2/12-027)

2012-02-14 Documentation for Two Characters FE2B and FE2C for Caucasian Albanian (N4131R) — Michael Everson, Jost Gippert ( WG2 N4243)

2012-07-31 Proposal to add Combining Up Tack Above to the UCS — Michael Everson, David Starner ( WG2 N4279,  L2/12-209)

2013-01-29 Cedillas and commas below — Eric Muller ( WG2 N4449,  L2/13-037)

2013-03-29 Transition Considerations — Lisa Moore ( WG2 N4448,  L2/13-053)

2013-06-07 Lithuanian Accents - Follow-Up — Deborah Anderson ( WG2 N4452)

2013-07-30 Comments on cedilla and comma below — Denis Moyogo Jacquerye ( L2/13-155)

2013-11-07 Cedillas and commas below, take 2 — Eric Muller ( WG2 N4536,  L2/13-225)

2014-12-04 Towards a Consensus Encoding of Newa — Ken Whistler (  L2/14-285)

2016-07-06 Representative glyph and annotation additions for U+033B — Lorna P. Evans, Patricia Keating ( L2/16-178)

Recommendations to UTC #148 August 2016 on Script Proposals — Deborah Anderson, Ken Whistler, Rick McGowan, Roozbeh Pournader, Andrew Glass, Laurentiu Iancu, and Lisa Moore ( L2/16-216) (See section 18 for recommendations)

UTC #148 Minutes ( L2/16-203) (See C.4 for decision and action items)