code: private void toPrettyString(int indentLevel, StringBuilder buf) {
      for (int i = 0; i < indentLevel; i++) {
        buf.append("  ");
      }
      buf.append(shortName).append(": ").append(targetPatterns);
      for (GrammaticalRelation child : children) {
        buf.append('\n');
        child.toPrettyString(indentLevel + 1, buf);
      }
    }
docs: Returns a <code>String</code> representation of this
  <code>GrammaticalRelation</code> and the hierarchy below
  it, with one node per line, indented according to
  <code>indentLevel</code>.
  
  @param indentLevel how many levels to indent (0 for root node)