``` class MainTemplate : Template<HTML> { ...

# ktor

[orangy]

class MainTemplate : Template<HTML> {
    val content = Placeholder<BODY>()
    val menu = TemplatePlaceholder<MenuTemplate>()
    override fun HTML.apply() {
        head {
            title { +"Template" }
        }
        body {
            h1 {
                insert(content)
            }
            insert(MenuTemplate(), menu)
        }
    }
}

class MulticolumnTemplate(val main: MainTemplate) : Template<HTML> {
    val column1 = Placeholder<FlowContent>()
    val column2 = Placeholder<FlowContent>()
    override fun HTML.apply() {
        insert(main) {
            content {
                div("column") {
                    insert(column1)
                }
                div("column") {
                    insert(column2)
                }
            }
        }
    }
}

Something like this?