Ah shoot! While the advice in the above post is sound, the code won't work because "\w" includes "_"! Fix: 
/^([a-zA-Z0-9+])(?:_(\w+))?$/

[download]

or 

/^((?:(?!_)\w)+)(?:_(\w+))?$/

[download]

In reply to Re^2: simple regexp problem by ikegami
in thread simple regexp problem by jeanluca

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