What ］ means
It closes a bracketed passage. Japanese technical text can use ［…］ to set off a term or insertion.
Square brackets grouped formulas in print around 1550–1593, though accounts differ on who introduced them. Japanese print adopted the family through Western-influenced typography in the 19th century. In technical text, ［…］ can mark an interface label; 「…」 marks quotations.
NFKC maps ］ to ]. This Unicode compatibility-normalization form folds the width distinction. The separate character remains for compatibility with older East Asian encodings that distinguished one-cell and two-cell forms.
Neutral punctuation for Japanese technical text.
In code, ］ and ] are distinct characters.
Don't confuse it with
2Questions 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 ］
］\FF3DCodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.