public Document setDocType(DocType docType) {
    if (docType == null) {
      // Remove any existing doctype
      int docTypeIndex = content.indexOfDocType();
      if (docTypeIndex >= 0) content.remove(docTypeIndex);
      return this;
    }

    if (docType.getParent() != null) {
      throw new IllegalAddException(docType,
                                    "The DocType already is attached to a document");
    }

    // Add DocType to head if new, replace old otherwise
    int docTypeIndex = content.indexOfDocType();
    if (docTypeIndex < 0) {
      content.add(0, docType);
    }
    else {
      content.set(docTypeIndex, docType);
    }

    return this;
  }
public Document setDocType(DocType docType)