question: public final TextBuilder append ( char chars [ ] , int offset , int length ) { final int end = offset + length ; if ( ( offset < 0 ) || ( length < 0 ) || ( end > chars . length ) ) throw new IndexOutOfBoundsException ( ) ; int newLength = _length + length ; while ( _capacity < newLength ) { increaseCapacity ( ) ; } for ( int i = offset , j = _length ; i < end ; ) { char [ ] dstChars = _high [ j > > B1 ] ; int dstBegin = j & M1 ; int inc = Math . min ( C1 - dstBegin , end - i ) ; System . arraycopy ( chars , i , dstChars , dstBegin , inc ) ; i += inc ; j += inc ; } _length = newLength ; return this ; }
target:  Appends the characters from a subarray of the char array argument.