```javascript
document.addEventListener('DOMContentLoaded', function() {
    // Handle tab switching
    document.querySelectorAll('.nav-link').forEach(tab => {
        tab.addEventListener('click', function(e) {
            e.preventDefault();
            document.querySelectorAll('.nav-link').forEach(t => t.classList.remove('active'));
            this.classList.add('active');
            // Here you would load the sections for the selected tab
        });
    });

    // Handle section selection
    document.querySelectorAll('.list-group-item').forEach(item => {
        item.addEventListener('click', function() {
            document.querySelectorAll('.list-group-item').forEach(i => i.classList.remove('active'));
            this.classList.add('active');
            // Here you would load the notes for the selected section
        });
    });

    // Simulate loading notes when clicking sections
    document.querySelectorAll('.list-group-item').forEach(section => {
        section.addEventListener('click', function() {
            const editorFrame = document.querySelector('iframe');
            editorFrame.src = 'editor.html';
        });
    });
});
```