Well, since any string either has white space at the beginning, or it is without white space at the beginning, the question as you ask it is just "how do I match any string".

    /(?=)/
[download]

Will do that, but that's probably not what you want.

I could look at your example, but then I'd come up with the regexp:

    /^ ?<result>$/
[download]

That would match the two strings mentioned in the example, and nothing else. Which may be what you want, but I doubt it.

You know, 98% of the regex questions can be solved by defining what you want - once you do that, the regexp follows easily.