Geben Sie ein Beispiel für die XML-Definition eines GTK-Fensters für eine To-Do-Listenanwendung. Das UI-Design sollte den Designrichtlinien von Gnome folgen.
Here's an example of XML code defining a GTK window for a To-Do list application that follows Gnome's design guidelines:

```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE interface PUBLIC "-//GNOME//DTD Gtk 3.0//EN"
  "http://developer.gnome.org/dtd/3.0/gtk.dtd">
<interface>
  <object class="GtkWindow" id="main-window">
    <property name="title">To-Do List</property>
    <property name="default-width">600</property>
    <property name="default-height">400</property>
    <child>
      <object class="GtkBox" id="main-box">
        <property name="orientation">vertical</property>
        <child>
          <object class="GtkEntry" id="new-item-entry">
            <property name="hexpand">true</property>
            <property name="placeholder-text">Add a new item</property>
          </object>
        </child>
        <child>
          <object class="GtkScrolledWindow" id="item-list-scroll">
            <property name="hexpand">true</property>
            <property name="vexpand">true</property>
            <child>
              <object class="GtkListBox" id="item-list">
                <property name="selection-mode">none</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkButtonBox" id="button-box">
            <property name="layout-style">spread</property>
            <property name="halign">end</property>
            <child>
              <object class="GtkButton" id="add-button">
                <property name="label">Add</property>
              </object>
            </child>
            <child>
              <object class="GtkButton" id="delete-button">
                <property name="label">Delete</property>
                <property name="sensitive">false</property>
              </object>
            </child>
          </object>
        </child>
      </object>
    </child>
  </object>
</interface>
```

In this example, the XML code defines a GTK window with a vertical box layout containing three child elements: an entry box for adding new items, a scrolled window containing a list box of items, and a button box containing "Add" and "Delete" buttons. The code also sets properties for various elements, such as the window title, default size, and button labels. The design follows Gnome's guidelines for spacing, alignment, and layout style.