A template layout keeps shared page elements—such as headers, footers, titles, and navigation—in one stable wrapper while replacing an inner content region for each route. This avoids copying common HTML across pages and makes later changes easier. section 7.3.2
A Flask index template
An Index.html file can retain the document structure and provide a content block: {% block content %}{% endblock %}. Individual pages supply the route-specific material inside that region, while the surrounding header and footer remain unchanged. section 7.3.2
