This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+21CA forms with similar adjacent characters prevents a line break inside it.
The CLDR project calls this character “downwards paired arrows” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: arrows, downwards, paired.
The Wikipedia has the following information about this codepoint:
An arrow is a graphical symbol, such as ← or →, or a pictogram, used to point or indicate direction. In its simplest form, an arrow is a triangle, chevron, or concave kite, usually
affixed to a line segment or rectangle, and in more complex forms a representation of an actual arrow (e.g. ➵ U+27B5). The direction indicated by an arrow is the one along the length of the line or rectangle toward the single pointed end.
Representations
System
Representation (click value to copy)
Nº
8650
UTF-8
E2 87 8A
UTF-16
21 CA
UTF-32
00 00 21 CA
URL-Quoted
%E2%87%8A
HTML hex reference
⇊
Wrong windows-1252 Mojibake
⇊
HTML named entity
⇊
HTML named entity
⇊
Encoding: GB18030 (hex bytes)
81 36 CC 32
LATEX
\downdownarrows
RFC 5137
\u'21CA'
Bash and Zsh inside echo -e
\u21CA
C and C++
\u21CA
C#
\u21CA
CSS
\0021CA
Excel
=UNICHAR(8650)
Go
\u21CA
JavaScript
\u21CA
Modern JavaScript since ES6
\u{21ca}
JSON
\u21CA
Java
\u21CA
Lua
\u{21CA}
Matlab
char(8650)
Perl
"\x{21CA}"
PHP
\u{21ca}
PostgreSQL
U&'\21CA'
PowerShell
`u{21CA}
Python
\u21CA
Ruby
\u{21ca}
Rust
\u{21ca}
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