This character is a Nonspacing Mark and inherits its script property from the preceding character. It is also used in the scripts Arabic, Syriac.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Nonspacing Mark. When changing direction it is not mirrored. U+0651 prohibits a line break before it. The glyph can be confused with 9 other glyphs.
The Wikipedia has the following information about this codepoint:
Shaddah (Arabic: شَدّةshaddah[ˈʃæd.dæ], "[sign of] emphasis", also called by the verbal noun from the same root, tashdidتشديدtashdīd "emphasis") is one of the diacritics used with the Arabic alphabet, indicating a geminated consonant. It is functionally equivalent to writing a consonant twice in the orthographies of languages like Latin, Italian, Swedish, and Ancient Greek, and is thus rendered in Latin script in most schemes of Arabic transliteration, e.g. رُمّان = rummān 'pomegranates'.
Representations
System
Representation (click value to copy)
Nº
1617
UTF-8
D9 91
UTF-16
06 51
UTF-32
00 00 06 51
URL-Quoted
%D9%91
HTML hex reference
ّ
Wrong windows-1252 Mojibake
◌ّ
Encoding: CP720 (hex bytes)
91
Encoding: CP864 (hex bytes)
F1
Encoding: CP1256 (hex bytes)
F8
Encoding: GB18030 (hex bytes)
81 31 88 31
Encoding: ISO8859_6 (hex bytes)
F1
Encoding: CP420 (hex bytes)
42
Adobe Glyph List
afii57457
Adobe Glyph List
shaddaarabic
digraph
3+
RFC 5137
\u'0651'
Bash and Zsh inside echo -e
\u0651
C and C++
\u0651
C#
\u0651
CSS
\000651
Excel
=UNICHAR(1617)
Go
\u0651
JavaScript
\u0651
Modern JavaScript since ES6
\u{651}
JSON
\u0651
Java
\u0651
Lua
\u{651}
Matlab
char(1617)
Perl
"\x{651}"
PHP
\u{651}
PostgreSQL
U&'\0651'
PowerShell
`u{651}
Python
\u0651
Ruby
\u{651}
Rust
\u{651}
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