/^(?:Hello One World|Hello World|HelloWorld|Hello One Two World|Hello 
+Two Three World|Hello One Three World)$/

[download]
No, that was a joke ;)

If the ordering of One, Two, and Three is important, you could use something like

/Hello(?: One)?(?: Two)?(?: Three)? ?World/

[download]

In reply to Re: Regex Problem by choroba
in thread Regex Problem by Anonymous Monk

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