From the documentation:

Word Character: \w

\w matches any word character. A word character is a member of any of the Unicode categories listed in the following table.

• Ll (Letter, Lowercase)
• Lu (Letter, Uppercase)
• Lt (Letter, Titlecase)
• Lo (Letter, Other)
• Lm (Letter, Modifier)
• Nd (Number, Decimal Digit)
• Pc (Punctuation, Connector)
  • This category includes ten characters, the most commonly used of which is the LOWLINE character (_), u+005F.

If ECMAScript-compliant behavior is specified, \w is equivalent to [a-zA-Z_0-9].

See also

• Unicode Character Database
• Unicode Characters in the ‘Punctuation, Connector’ Category