`*`、`+`、`?`

Quantifiers tell the engine how many times to repeat the element that precedes them. The three basic quantifiers are *, +, ?.

They apply to the last atom: a single character (a+), a class (\d+), a group ((ab)+, module 4).

Pattern: \d+
Sample:  Codici 7, 12 e 314.
                ^  ^^    ^^^

\d+ matches "one or more digits", it does not stop at the first one: a maximal sequence of consecutive digits.

Deep dive into the optional quantifier

The question mark ? applies only to the single character immediately preceding it. To make an entire sequence of characters or words optional, you must enclose them in parentheses, for example (https)?.

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Review exercise

Additional challenge