U005B

U+005B is the Unicode code point for the left square bracket, the character with the graphical form "[". It resides in the Basic Latin block and corresponds to the ASCII value 0x5B (decimal 91). In Unicode and UTF-8, this character is encoded as a single byte 0x5B.

In computing, the left square bracket is a common delimiter. It starts array literals in languages such as JavaScript and many data-serialization formats, and it is used to indicate indexing or subscripting in expressions like array[i] or object["property"]. In mathematics and formal notation, a left bracket is used to begin open intervals or to group terms in expressions.

In programming and text processing, the bracket has special meaning in certain contexts. In regular expressions, [ begins a character class, and within strings it often requires escaping to avoid misinterpretation. In shell scripting, [ is a built-in test command (often used as [ condition ]; the closing bracket is essential for the command’s syntax). In most markup and data formats, it is treated as a ordinary character unless the surrounding syntax designates it as a delimiter or metacharacter.

For interoperability, the character is also represented in non-Unicode contexts as percent-encoded in URLs as %5B and as a numeric character reference in HTML as [. Related characters include U+005D for the right square bracket and U+005C for the backslash.

Overall, U+005B denotes a widely used punctuation mark with diverse roles across programming, mathematics, and data representation.