The advanced view, the route map and header actions

1. The route mapCopy Anchor Link

A Redirect\Map item (pool redirects) in etc/adminhtml/di.xml is keyed by the stock full action name and names the Light route. params copies request parameters, condition decides per request, module gates it. Returns maps the RMA grid and edit screen:

<item name="rma_rma_index" xsi:type="array">
    <item name="route" xsi:type="string">light/returns/index</item>
    <item name="module" xsi:type="string">MageOS_RMA</item>
</item>

The map works both ways: the Light page's mode switch opens the stock screen through Map::reverse(). one_way leaves an entry out of the reverse direction.

2. The light route ruleCopy Anchor Link

The map only redirects to controllers on the admin front name light, and only in simple mode. Your controllers join that route with before="Mrx_Light", under a folder named after your module (Light developer guide).

3. Links into the advanced viewCopy Anchor Link

AdvancedUrlInterface::get() builds a link to a stock screen that stays open in simple mode, with the Light top bar around it. It adds this parameter:

public const PARAM = 'mrx_stock';

A nav or palette item with advanced true opens its stock route that way and shows "Opens in the advanced view". Acme_LightProof adds one under Customers:

<item name="advanced" xsi:type="boolean">true</item>

4. The way backCopy Anchor Link

On a stock screen opened in the advanced view, the banner links back to the Light page. The map gives most screens their way back. A module whose stock screens don't map one to one registers a class that implements BackLinkProviderInterface in the AdvancedView argument providers (pool back_link_providers), or a section in the argument sections (pool back_link_sections) that names a Light route for a group of stock screens.

public function getBackLink(string $fullActionName): ?array;

• It returns label, the whole link text ("Back to Apps"), url, and optionally text, which replaces the line under the banner's title ("Every setting is here, …"). Null leaves it to the next provider.
• The banner takes the first answer from, in order: the route map, the referer, the Light page that opened the stock flow, the providers (by sort_order, default 100), the sections, the nav item, and Home. When the referer or that Light page is the very page a provider links to (the same route, controller and action), the provider's link wins: it names the spot on that page, as Back to Apps opens the app's row.
• A provider that throws, or answers an unsafe url or an empty label, is skipped.

5. The mode in codeCopy Anchor Link

ModeInterface tells your code which mode the admin works in, in the admin area only:

public function isStockView(): bool;

Layout uses the handles mrx_simple and mrx_advanced instead. Your own Light pages show the "Only available in the advanced view" hint with the AdvancedHint block (A settings page from your system.xml).

6. Header actions on other modules' pagesCopy Anchor Link

A PageHeader\ActionPool item (pool header_actions) is keyed by the page's full action name, then by your key. It always lands in More actions; there is no key to put it elsewhere. condition names a class that implements ActionConditionInterface. Since 0.3.0, target _blank opens the link in a new tab (target="_blank" rel="noopener"), for a screen outside the admin such as a visual editor; any other value is ignored and the link opens in the same tab. Use it where leaving the page would drop the admin's place, and say so in the label when it isn't obvious. Acme_LightProof adds "Open proof" to the product editor:

<item name="acme_proof_open" xsi:type="array">
    <item name="label" xsi:type="string" translate="true">Open proof</item>

Acme_LightProof's top-level nav item, b2b category and default pin prove the mechanism; they are not a pattern to copy (An app, its category and pins).