code: public void append(StringConcatenation concat, String indentation) {
  		if (indentation.isEmpty()) {
  			append(concat);
  		} else if (concat != null)
  			appendSegments(indentation, segments.size(), concat.getSignificantContent(), concat.lineDelimiter);
  	}
docs: Append the contents of a given StringConcatenation to this sequence. Does nothing
  if the concatenation is <code>null</code>. The given indentation will be prepended to each line except
  the first one.
  
  @param concat
  the to-be-appended StringConcatenation.
  @param indentation
  the indentation string that should be prepended. May not be <code>null</code>.
  @since 2.11