[All Hosts] (devx) clarify feature filtering on older versions (#5127)

* [All Hosts] (devx) clarify feature filtering on older versions

* clarify

* typo

* add section for contentRuntimes

* fix

* replace pronoun

* Apply suggestions from code review

Co-authored-by: Elizabeth Samuel <[email protected]>

---------

Co-authored-by: Elizabeth Samuel <[email protected]>

Author: Rick-Kirkham

docs/develop/requirements-property-unified-manifest.md

@@ -1,7 +1,7 @@
 ---
 title: Specify Office Add-in requirements in the unified manifest for Microsoft 365
 description: Learn how to use requirements to configure on which host and platforms an add-in can be installed and which features are available.
-ms.date: 02/12/2025
+ms.date: 04/18/2025
 ms.topic: how-to
 ms.localizationpriority: medium
 ---
@@ -53,6 +53,13 @@ The "requirements" properties in descendant objects of "extensions" are used to
 > [!TIP]
 > Don't include a capability, formFactor, or scope requirement in a descendant object of "extensions" that's *less* restrictive than the corresponding capability, formFactor, or scope requirement in the ancestor "extensions.requirements" property, if there is one. Since the add-in can't be installed on clients that don't meet the ancestor requirement, no feature filtering would occur anyway. For example, if an "extensions.requirements.capabilities" property requires **Mailbox 1.10**, there's no point in requiring **Mailbox 1.9** in any descendant objects.
 
+> [!NOTE]
+> Office Add-ins that use the unified manifest for Microsoft 365 are *directly* supported in Office on the web, in [new Outlook on Windows](https://support.microsoft.com/office/656bb8d9-5a60-49b2-a98b-ba7822bc7627), and in Office on Windows connected to a Microsoft 365 subscription, Version 2304 (Build 16320.00000) or later.
+>
+> When the app package that contains the unified manifest is deployed in [AppSource](https://appsource.microsoft.com/) or the [Microsoft 365 Admin Center](/office/dev/add-ins/publish/publish) then an add-in only manifest is generated from the unified manifest and stored. This add-in only manifest enables the add-in to be installed on platforms that don't directly support the unified manifest, including Office on Mac, Office on mobile, subscription versions of Office on Windows earlier than 2304 (Build 16320.00000), and perpetual versions of Office on Windows.
+>
+> Feature filtering is less fine-grained in the add-in only manifest. As a result, on platforms that don't directly support the unified manifest, adding a "requirements" subproperty to *any* child of "extensions" is effectively the same as adding that same "requirements" subproperty to *all* the children of "extensions" with one possible exception. So, on these platforms *none* of the features that are configured in these child properties of "extensions" will be available on platform and version combinations that don't meet the specified requirements. The exception is the "extensions.alternates" property. If this property is present, the alternates feature will be filtered in or out based only on its own "requirements" subproperty (if any), not on the "requirements" subproperties of any other child properties of "extensions".
+
 ### extensions.alternates.requirements
 
 The "extensions.alternates" property enables add-in developers to do the following:
@@ -61,14 +68,9 @@ The "extensions.alternates" property enables add-in developers to do the followi
 - Either hide or give preference to the version that uses the older technology.
 - Specify icons that are needed to make the unified manifest version of the add-in installable on Office versions that don't directly support the unified manifest.
 
-> [!NOTE]
-> Office Add-ins that use the unified manifest for Microsoft 365 are *directly* supported in Office on the web, in [new Outlook on Windows](https://support.microsoft.com/office/656bb8d9-5a60-49b2-a98b-ba7822bc7627), and in Office on Windows connected to a Microsoft 365 subscription, Version 2304 (Build 16320.00000) or later.
->
-> When the app package that contains the unified manifest is deployed in [AppSource](https://appsource.microsoft.com/) or the [Microsoft 365 Admin Center](/office/dev/add-ins/publish/publish) then an add-in only manifest is generated from the unified manifest and stored. This add-in only manifest enables the add-in to be installed on platforms that don't directly support the unified manifest, including Office on Mac, Office on mobile, subscription versions of Office on Windows earlier than 2304 (Build 16320.00000), and perpetual versions of Office on Windows.
-
 For more information, see [Manage both a unified manifest and an add-in only manifest version of your Office Add-in](/office/dev/add-ins/concepts/duplicate-legacy-metaos-add-ins).
 
-The "requirements" subproperty of "extensions.alternates" to selectively apply the "hide" or "prefer" subproperties only when certain requirements are met.
+Use the "requirements" subproperty of "extensions.alternates" to selectively apply the "hide" or "prefer" subproperties only when certain requirements are met.
 
 For example, suppose that you want to hide (from the Office UI for installing add-ins) an older version of your add-in, but only in Office versions that support the **Mailbox 1.10** requirement set. You could do that with markup similar to the following:
 
@@ -137,6 +139,10 @@ For example, suppose an Outlook add-in is configured to autolaunch in response t
 ]
 ```
 
+### extensions.contentRuntimes.requirements
+
+The "extensions.contentRuntimes" property can't be combined with any other child property of "extensions" (except "extensions.requirements"). This means that the content is the *only* feature of the add-in, so it makes no sense to filter out the feature's availability on some combinations of platform and Office version while allowing add-in to be installable on those same combinations. Accordingly, don't use the "requirements" property in "contentRuntimes". To control the installability of the content add-in, use the "extensions.requirements" property of the parent "extensions".
+
 ### extensions.contextMenus.requirements
 
 The "extensions.contextMenus" property configures the add-in's context menus. A context menu is a shortcut menu that appears when you right-click (or select and hold) in the Office UI. The "requirements" subproperty can be used to allow context menus only when certain requirements are met.