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Because the code framework in this challenge uses Matcher.find(), and that returns true if the pattern can match any substring in the target. Without the start and end anchors, any invalid username that also had a valid username inside of itself would get approved.
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Valid Username Regular Expression
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Because the code framework in this challenge uses
Matcher.find(), and that returns true if the pattern can match any substring in the target. Without the start and end anchors, any invalid username that also had a valid username inside of itself would get approved.