Suppose you have a repeated pattern, such as "(?:...)*" or "(?:...){0,100}".

If, after matching the subpattern, the text position hasn't changed, and none of the capture groups have changed, then there has been no progress, and the subpattern will be matched again with no more progress, unless the maximum count has been reached, at which point it'll continue with the remainder of the pattern. If there's no minimum count, then the subpattern will be matched repeatedly forever.

Therefore, what a repeat should do is not to attempt any more iterations if the text position hasn't changed and none of the capture groups have changed.