username constant
begin with one letter, contains only alphanumeric and only one dot or underscore in a row (not accept at the end)
Implementation
static const Pattern username = r'^[a-zA-Z](?:[_.]?[a-zA-Z0-9]+)*$'
begin with one letter, contains only alphanumeric and only one dot or underscore in a row (not accept at the end)
static const Pattern username = r'^[a-zA-Z](?:[_.]?[a-zA-Z0-9]+)*$'