A Storefront is designed so that multiple pages share a common header and footer layout.

For designing a storefront where multiple pages share a common header and footer layout without repeating code, the correct ISML tag to use is <isinclude>. This tag allows the developer to include a common template into other templates where needed. Using <isinclude> ... </isinclude> ensures that the header and footer are managed in single, central templates and are consistently applied across different pages, making the site maintenance easier and code more efficient by avoiding duplication.