< isdecorate > is the correct ISML construct for applying a reusable page layout to multiple templates. A decorator template can contain the common page shell, header, navigation, footer, scripts, and structural markup, while the individual child page contains only page-specific content.
Salesforce explicitly identifies a common header-and-footer layout as atypical use casefor < isdecorate > . The decorator template contains < isreplace/ > , which marks the position where the child template ' s enclosed content is inserted.
Option A is therefore not the tag normally placed around each page ' s content; < isreplace/ > belongs inside the decorator template itself. Option C can insert another template fragment, but using repeated includes for headers and footers does not provide the same centralized page-layout structure and composition semantics.
Decorator-based design improves maintainability because common markup is maintained once. If the header or footer changes, developers update the decorator rather than making the same structural changes across every individual storefront page.
Study Guide reference:Application Development — ISML decorators, < isdecorate > , < isreplace > , template reuse, common layouts, and storefront maintainability.
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