pattern property
pattern is a regex that is used to match the national (significant) number. For example, the pattern "(20)(\d{4})(\d{4})" will match number "2070313000", which is the national (significant) number for Google London. Note the presence of the parentheses, which are capturing groups what specifies the grouping of numbers.
Implementation
@$pb.TagNumber(1)
$core.String get pattern => $_getSZ(0);