Common characer classes

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• \d digit: [0-9] or Unicode Characters in the 'Number, Decimal Digit' Category
• \w word character [a-zA-Z0-9_] (digits, letters, underscore) or see the Unicode set of digits and letters
• \s white space: [\f\t\n\r\v ] form-feed, tab, newline, carriage return, vertical-tab, and SPACE

• Use stand alone: \d or as part of a larger character class: [abc\d]