Illustrative structure. The walk visits every term and connector in drawing order; no input is matched or parsed.

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Structural exploration

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Colour tags Railroad diagram of the regular expression (?:red|green|blue)(?:-(?:light|dark))?(?:,[a-z]+)* with 8 terms. It shows structure; it does not match input. Colour tags non-capturing group non-capturing group non-capturing group non-capturing group red green blue - light dark , one of a-z pattern