usernameV2 property
Username regex (v2)
May start with @ Minimum 3 characters Allowed to use aplhanumeric, underscore ("_"), dash ("-"), and period (".") characters. Has only one symbols in a row. Symbols can only be used in the middle of name.
Implementation
static String usernameV2 =
r'^(?!.*[_\.\-]{2})@?[a-zA-Z0-9][a-zA-Z0-9_\.\-]+[a-zA-Z0-9]$';