This character is a Other Letter and is mainly used in the Lycian script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+1028F forms with similar adjacent characters prevents a line break inside it.
The Wikipedia has the following information about this codepoint:
The Lycian alphabet was used to write the Lycian language of the Asia Minor region of Lycia. It was an extension of the Greek alphabet, with half a dozen additional letters for sounds not found in Greek. It was largely similar to the Lydian and the Phrygian alphabets.
Representations
System
Representation (click value to copy)
NΒΊ
66191
UTF-8
F0 90 8A 8F
UTF-16
D8 00 DE 8F
UTF-32
00 01 02 8F
URL-Quoted
%F0%90%8A%8F
HTML hex reference
𐊏
Wrong windows-1252 Mojibake
Γ°ΒΕ Β
Encoding: GB18030 (hex bytes)
90 30 C2 35
RFC 5137
\u'1028F'
Bash and Zsh inside echo -e
\U0001028F
C and C++
\U0001028F
C#
\U0001028F
CSS
\01028F
Excel
=UNICHAR(66191)
Go
\U0001028F
JavaScript
\uD800\uDE8F
Modern JavaScript since ES6
\u{1028f}
JSON
\uD800\uDE8F
Java
\uD800\uDE8F
Lua
\u{1028F}
Matlab
char(66191)
Perl
"\x{1028F}"
PHP
\u{1028f}
PostgreSQL
U&'\+01028F'
PowerShell
`u{1028F}
Python
\U0001028F
Ruby
\u{1028f}
Rust
\u{1028f}
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