question: public static final String digitsAndPlusOnly ( Matcher matcher ) { StringBuilder buffer = new StringBuilder ( ) ; String matchingRegion = matcher . group ( ) ; for ( int i = 0 , size = matchingRegion . length ( ) ; i < size ; i ++ ) { char character = matchingRegion . charAt ( i ) ; if ( character == '+' || Character . isDigit ( character ) ) { buffer . append ( character ) ; } } return buffer . toString ( ) ; }
target:  Convenience method to return only the digits and plus signs in the matching string.