code: public StrBuilder deleteCharAt(final int index) {
          if (index < 0 || index >= size) {
              throw new StringIndexOutOfBoundsException(index);
          }
          deleteImpl(index, index + 1, 1);
          return this;
      }
docs: Deletes the character at the specified index.
  
  @see #charAt(int)
  @see #setCharAt(int, char)
  @param index  the index to delete
  @return this, to enable chaining
  @throws IndexOutOfBoundsException if the index is invalid