Username Regex List

Hi,

I hope we can start share a collection of some regex for username here;

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From: Title

Descriptions: Accept only alphanumeric values and hyphen, underscore or period (-/_/.). Start from alphanumeric character not a hyphen or underscore.

^[a-z][-_a-z0-9]*$
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Descriptions: It verifies that: - Only letters, numbers and period,hyphen & underscore are allowed - No two different symbols may follow each other - Cannot begin or end with a symbol,hyphen, underscore or dot.

Problem: No character limitation.

^((([A-Za-z0-9]+_)|([A-Za-z0-9]+\-)|([A-Za-z0-9]+\.))*([A-Za-z0-9])){5,15}$
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Hope u guys can add more options, thanks