Regular Expression for a repeating pattern?

I've got some data input by a user.
it's like <span>&nbsp; &nbsp; </span> and this can be any number of this non-breaking space up until the close of the span tag, with nothing else.
I'm trying to figure out a reasonable way to be able to detect an occurance of a span like this. It would be the span and then 30 occurances of the non-breaking space, or it could be 300 occurances, or any number between.
I was hoping there'd be a way to detect this repeating pattern within a regular expression.

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