hansgafriedzal · March 23, 2018 04:44
diff --git a/regex-username-validation.txt b/regex-username-validation.txt
 ^(?![_.])(?!.*[_.]{2})[a-zA-Z0-9._]{4,20}(?<![_.])$
 └──┬───┘└──────┬────┘└─────────┬───────┘└──┬────┘
    │           │               │           no _ or . at the end
    │           │               allowed chars & length
    │           no __ or _. or ._ or .. inside
    no _ or . at the beginning
	^(?![_.])(?!.*[_.]{2})[a-zA-Z0-9._]{4,20}(?<![_.])$
	└──┬───┘└──────┬────┘└─────────┬───────┘└──┬────┘
	│ │ │ no _ or . at the end
	│ │ allowed chars & length
	│ no __ or _. or ._ or .. inside
	no _ or . at the beginning