code: public char charAt(int where) {
          int len = length();
          if (where < 0) {
              throw new IndexOutOfBoundsException("charAt: " + where + " < 0");
          } else if (where >= len) {
              throw new IndexOutOfBoundsException("charAt: " + where + " >= length " + len);
          }
  
          if (where >= mGapStart)
              return mText[where + mGapLength];
          else
              return mText[where];
      }
docs: Return the char at the specified offset within the buffer.