question: public EncoderTestSuiteBuilder valid ( String chars ) { for ( int i = 0 , n = chars . length ( ) ; i < n ; ++ i ) { char ch = chars . charAt ( i ) ; _valid . set ( ch ) ; _invalid . clear ( ch ) ; _encoded . clear ( ch ) ; } return this ; }
target:  Tells the builder that a character set is valid and unescaped.