Add Nested Views page under View section

https://claude.ai/code/session_0188k14QNhv7aWeXMPQHmxZo

Author: claude

docs/.vitepress/config.mjs

@@ -134,6 +134,7 @@ export default defineConfig({
             collapsed: true,
             items: [
               { text: "Definition", link: "/development/view/definition" },
+              { text: "Nested", link: "/development/view/nested" },
               { text: "Expression Binding", link: "/development/model/expression_binding" },
               { text: "Formatter", link: "/development/specific/formatter" },
             ],

docs/development/view/nested.md

@@ -0,0 +1,100 @@
+---
+outline: [2, 4]
+---
+# Nested Views
+
+A nested view is a view that is built from several independent parts. In abap2UI5 there are two main ways to achieve this: composing a single view tree from helper methods, and splitting the app into sub-apps that each own a slice of the view.
+
+#### Composing with Helper Methods
+
+The fluent builder returns each node as an object reference, so you can pass a node into a helper method and let it add children there:
+
+```abap
+METHOD z2ui5_if_app~main.
+  IF client->check_on_init( ).
+    DATA(xml)  = z2ui5_cl_xml_view=>factory( ).
+    DATA(page) = xml->shell( )->page( 'My App' ).
+
+    build_header( page ).
+    build_content( page ).
+    build_footer( page ).
+
+    client->view_display( xml->stringify( ) ).
+  ENDIF.
+ENDMETHOD.
+
+METHOD build_header.
+  io_page->toolbar( )->title( 'Header' ).
+ENDMETHOD.
+
+METHOD build_content.
+  io_page->vbox(
+      )->text( 'Line 1'
+      )->text( 'Line 2' ).
+ENDMETHOD.
+
+METHOD build_footer.
+  io_page->footer( )->button(
+    text  = 'Save'
+    press = client->_event( 'SAVE' ) ).
+ENDMETHOD.
+```
+
+Each helper receives the parent node by reference and attaches its controls to it. The final `stringify( )` call serialises the entire tree — including all nested children — into one XML string.
+
+#### Sub-Apps
+
+For larger apps it is useful to split responsibility across separate ABAP classes. Each sub-app implements `z2ui5_if_app` and manages its own piece of the view. The parent app instantiates the sub-app, passes the client, and merges the returned view fragment into its own view tree.
+
+**Parent app:**
+```abap
+METHOD z2ui5_if_app~main.
+  IF client->check_on_init( ).
+    sub_app = NEW z2ui5_cl_my_sub_app( ).
+  ENDIF.
+
+  DATA(xml)  = z2ui5_cl_xml_view=>factory( ).
+  DATA(page) = xml->shell( )->page( 'Parent' ).
+
+  " Let the sub-app render into a container on the page
+  DATA(container) = page->vbox( ).
+  sub_app->render( client = client io_node = container ).
+
+  client->view_display( xml->stringify( ) ).
+ENDMETHOD.
+```
+
+**Sub-app:**
+```abap
+METHOD render.
+  io_node->text( 'I am the sub-app' ).
+  io_node->button(
+    text  = 'Sub Action'
+    press = io_client->_event( 'SUB_ACTION' ) ).
+ENDMETHOD.
+```
+
+The sub-app appends its controls to whatever node the parent provides. Events fired inside the sub-app are handled by the sub-app's own `main` method on the next roundtrip.
+
+#### Navigation Between Views
+
+When the nested content changes completely — for example, a detail page replacing a list — use `view_display` to swap the entire view rather than nesting:
+
+```abap
+CASE client->get_event( ).
+  WHEN 'OPEN_DETAIL'.
+    client->view_display( detail_view->stringify( ) ).
+  WHEN 'BACK'.
+    client->view_display( list_view->stringify( ) ).
+ENDCASE.
+```
+
+Reserve true nesting for content that appears side-by-side or in a stable layout shell. Use `view_display` for sequential navigation where one screen fully replaces another.
+
+#### Tips
+
+- Keep each helper or sub-app focused on one logical section. A helper that grows beyond ~30 lines is a candidate for its own sub-app class.
+- Sub-apps can hold their own instance attributes for local state. Because the whole app tree is reconstructed on every roundtrip, each sub-app re-renders from its current state automatically.
+- Pass only the node the sub-app needs, not the whole view root. This limits the sub-app's scope and makes the boundary explicit.
+
+See `Z2UI5_CL_DEMO_APP_160` for an end-to-end example of parent and sub-app composition.