question: public static IFitsHeader lookup ( String key ) { int keyLength = key . length ( ) ; if ( keyLength > 0 && Character . isDigit ( key . charAt ( keyLength - 1 ) ) ) { StringBuilder builder = new StringBuilder ( ) ; for ( int index = 0 ; index < keyLength ; index ++ ) { char character = key . charAt ( index ) ; if ( Character . isDigit ( character ) ) { if ( builder . charAt ( builder . length ( ) - 1 ) != 'n' ) { builder . append ( 'n' ) ; } } else { builder . append ( character ) ; } } return STANDARD_KEYS . get ( builder . toString ( ) ) ; } return STANDARD_KEYS . get ( key ) ; }
target:  lookup a string key in the standard key sets.