question: public StrBuilder deleteFirst ( final String str ) { final int len = ( str == null ? 0 : str . length ( ) ) ; if ( len > 0 ) { final int index = indexOf ( str , 0 ) ; if ( index >= 0 ) { deleteImpl ( index , index + len , len ) ; } } return this ; }
target:  Deletes the string wherever it occurs in the builder.