What ⩴ means
In BNF, it means “is defined as.” BNF writes grammar rules: the expression after the sign defines the name before it. The glyph is the compact form of ::=.
A 2003 catalogue of named characters for web documents glossed it as “double colon, equals,” matching its construction.
Unicode’s NFKC and NFKD compatibility normalization expand ⩴ to ::=. Software applying either form changes one character into three.
Don't confuse it with
2::=
≔Three separate characters—two colons, then an equals sign; ⩴ is one.
Colon Equals
It has one colon before the equals sign; ⩴ has two.
Questions people ask
1Why does ⩴ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ⩴
Windows (Word)
Alt+XType 2A74, then Alt+X to get ⩴.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “double colon equal”.
Linux
Ctrl+Shift+UType 2a74, then Enter or Space.
HTML
⩴CSS
\2A74Codes and encoding1 code points
HTML decimal
⩴
HTML hex
⩴
CSS content
content: "\2A74";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%A9%B4
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.