content: import java.util.ArrayList;
  import java.util.List;
  import java.io.FileWriter;
  import java.io.IOException;
  
  // Interface for document elements
  interface DocumentElement {
      public abstract String render();
  }
  
  // Concrete implementation for text elements
  class TextElement implements DocumentElement {
      private String text;
  
      public TextElement(String text) {
          this.text = text;
      }
  
      @Override
      public String render() {
          return text;
      }
  }
  
  // Concrete implementation for image elements
  class ImageElement implements DocumentElement {
      private String imagePath;
  
      public ImageElement(String imagePath) {
          this.imagePath = imagePath;
      }
  
      @Override
      public String render() {
          return "[Image: " + imagePath + "]";
      }
  }
  
  // NewLineElement represents a line break in the document.
  class NewLineElement implements DocumentElement {
      @Override
      public String render() {
          return "\n";
      }
  }
  
  // TabSpaceElement represents a tab space in the document.
  class TabSpaceElement implements DocumentElement {
      @Override
      public String render() {
          return "\t";
      }
  }
  
  // Document class responsible for holding a collection of elements
  class Document {
      private List<DocumentElement> documentElements = new ArrayList<>();
  
      public void addElement(DocumentElement element) {
          documentElements.add(element);
      }
  
      // Renders the document by concatenating the render output of all elements.
      public String render() {
          StringBuilder result = new StringBuilder();
          for (DocumentElement element : documentElements) {
              result.append(element.render());
          }
          return result.toString();
      }
  }
  
  // Persistence Interface
  interface Persistence {
      void save(String data);
  }
  
  // FileStorage implementation of Persistence
  class FileStorage implements Persistence {
      @Override
      public void save(String data) {
          try {
              FileWriter outFile = new FileWriter("document.txt");
              outFile.write(data);
              outFile.close();
              System.out.println("Document saved to document.txt");
          } catch (IOException e) {
              System.out.println("Error: Unable to open file for writing.");
          }
      }
  }
  
  // Placeholder DBStorage implementation
  class DBStorage implements Persistence {
      @Override
      public void save(String data) {
          // Save to DB
      }
  }
  
  // DocumentEditor class managing client interactions
  class DocumentEditor {
      private Document document;
      private Persistence storage;
      private String renderedDocument = "";
  
      public DocumentEditor(Document document, Persistence storage) {
          this.document = document;
          this.storage = storage;
      }
  
      public void addText(String text) {
          document.addElement(new TextElement(text));
      }
  
      public void addImage(String imagePath) {
          document.addElement(new ImageElement(imagePath));
      }
  
      // Adds a new line to the document.
      public void addNewLine() {
          document.addElement(new NewLineElement());
      }
  
      // Adds a tab space to the document.
      public void addTabSpace() {
          document.addElement(new TabSpaceElement());
      }
  
      public String renderDocument() {
          if (renderedDocument.isEmpty()) {
              renderedDocument = document.render();
          }
          return renderedDocument;
      }
  
      public void saveDocument() {
          storage.save(renderDocument());
      }
  }
  
  // Client usage example
  public class DocumentEditorClient {
      public static void main(String[] args) {
          Document document = new Document();
          Persistence persistence = new FileStorage();
  
          DocumentEditor editor = new DocumentEditor(document, persistence);
  
          // Simulate a client using the editor with common text formatting features.
          editor.addText("Hello, world!");
          editor.addNewLine();
          editor.addText("This is a real-world document editor example.");
          editor.addNewLine();
          editor.addTabSpace();
          editor.addText("Indented text after a tab space.");
          editor.addNewLine();
          editor.addImage("picture.jpg");
  
          // Render and display the final document.
          System.out.println(editor.renderDocument());
  
          editor.saveDocument();
      }
  }
  