code: public StrBuilder delete(final int startIndex, int endIndex) {
          endIndex = validateRange(startIndex, endIndex);
          final int len = endIndex - startIndex;
          if (len > 0) {
              deleteImpl(startIndex, endIndex, len);
          }
          return this;
      }
docs: Deletes the characters between the two specified indices.
  
  @param startIndex  the start index, inclusive, must be valid
  @param endIndex  the end index, exclusive, must be valid except
  that if too large it is treated as end of string
  @return this, to enable chaining
  @throws IndexOutOfBoundsException if the index is invalid