Add (and document) injectedJavaScriptBeforeContentLoadedForMainFrameOnly and injectedJavaScriptForMainFrameOnly stub props for parity with iOS and macOS.

android/src/main/java/com/reactnativecommunity/webview/RNCWebViewManager.java

     ((RNCWebView) view).setInjectedJavaScriptBeforeContentLoaded(injectedJavaScriptBeforeContentLoaded);
   }
 
+  @ReactProp(name = "injectedJavaScriptForMainFrameOnly")
+  public void setInjectedJavaScriptForMainFrameOnly(WebView view, boolean enabled) {
+    ((RNCWebView) view).setInjectedJavaScriptForMainFrameOnly(enabled);
+  }
+
+  @ReactProp(name = "injectedJavaScriptBeforeContentLoadedForMainFrameOnly")
+  public void setInjectedJavaScriptBeforeContentLoadedForMainFrameOnly(WebView view, boolean enabled) {
+    ((RNCWebView) view).setInjectedJavaScriptBeforeContentLoadedForMainFrameOnly(enabled);
+  }
+
   @ReactProp(name = "messagingEnabled")
   public void setMessagingEnabled(WebView view, boolean enabled) {
     ((RNCWebView) view).setMessagingEnabled(enabled);
     String injectedJS;
     protected @Nullable
     String injectedJSBeforeContentLoaded;
+
+    /**
+     * android.webkit.WebChromeClient fundamentally does not support JS injection into frames other
+     * than the main frame, so these two properties are mostly here just for parity with iOS & macOS.
+     */
+    protected boolean injectedJavaScriptForMainFrameOnly = true;
+    protected boolean injectedJavaScriptBeforeContentLoadedForMainFrameOnly = true;
+
     protected boolean messagingEnabled = false;
     protected @Nullable
     RNCWebViewClient mRNCWebViewClient;
       injectedJSBeforeContentLoaded = js;
     }
 
+    public void setInjectedJavaScriptForMainFrameOnly(boolean enabled) {
+      injectedJavaScriptForMainFrameOnly = enabled;
+    }
+
+    public void setInjectedJavaScriptBeforeContentLoadedForMainFrameOnly(boolean enabled) {
+      injectedJavaScriptBeforeContentLoadedForMainFrameOnly = enabled;
+    }
+
     protected RNCWebViewBridge createRNCWebViewBridge(RNCWebView webView) {
       return new RNCWebViewBridge(webView);
     }

docs/Reference.md

 - [`source`](Reference.md#source)
 - [`automaticallyAdjustContentInsets`](Reference.md#automaticallyadjustcontentinsets)
 - [`injectedJavaScript`](Reference.md#injectedjavascript)
-- [`injectedJavaScriptBeforeContentLoaded`](Reference.md#injectedJavaScriptBeforeContentLoaded)
+- [`injectedJavaScriptBeforeContentLoaded`](Reference.md#injectedjavascriptbeforecontentloaded)
+- [`injectedJavaScriptForMainFrameOnly`](Reference.md#injectedjavascriptformainframeonly)
+- [`injectedJavaScriptBeforeContentLoadedForMainFrameOnly`](Reference.md#injectedjavascriptbeforecontentloadedformainframeonly)
 - [`mediaPlaybackRequiresUserAction`](Reference.md#mediaplaybackrequiresuseraction)
 - [`nativeConfig`](Reference.md#nativeconfig)
 - [`onError`](Reference.md#onerror)
 
 ---
 
+### `injectedJavaScriptForMainFrameOnly`
+
+If `true` (default; mandatory for Android), loads the `injectedJavaScript` only into the main frame.
+
+If `false`, (only supported on iOS and macOS), loads it into all frames (e.g. iframes).
+
+| Type   | Required | Platform |
+| ------ | -------- | -------- |
+| bool | No       | iOS and macOS (only `true` supported for Android) |
+
+---
+
+### `injectedJavaScriptBeforeContentLoadedForMainFrameOnly`
+
+If `true` (default; mandatory for Android), loads the `injectedJavaScriptBeforeContentLoaded` only into the main frame.
+
+If `false`, (only supported on iOS and macOS), loads it into all frames (e.g. iframes).
+
+| Type   | Required | Platform |
+| ------ | -------- | -------- |
+| bool | No       | iOS and macOS (only `true` supported for Android) |
+
+---
+
 ### `mediaPlaybackRequiresUserAction`
 
 Boolean that determines whether HTML5 audio and video requires the user to tap them before they start playing. The default value is `true`. (Android API minimum version 17).

src/WebViewTypes.ts

   incognito?: boolean;
   injectedJavaScript?: string;
   injectedJavaScriptBeforeContentLoaded?: string;
+  injectedJavaScriptForMainFrameOnly?: boolean;
+  injectedJavaScriptBeforeContentLoadedForMainFrameOnly?: boolean;
   mediaPlaybackRequiresUserAction?: boolean;
   messagingEnabled: boolean;
   onScroll?: (event: NativeScrollEvent) => void;
    */
   injectedJavaScriptBeforeContentLoaded?: string;
 
+  /**
+   * If `true` (default; mandatory for Android), loads the `injectedJavaScript` only into the main frame.
+   * If `false` (only supported on iOS and macOS), loads it into all frames (e.g. iframes).
+   */
+  injectedJavaScriptForMainFrameOnly?: boolean;
+
+  /**
+   * If `true` (default; mandatory for Android), loads the `injectedJavaScriptBeforeContentLoaded` only into the main frame.
+   * If `false` (only supported on iOS and macOS), loads it into all frames (e.g. iframes).
+   */
+  injectedJavaScriptBeforeContentLoadedForMainFrameOnly?: boolean;
+
   /**
    * Boolean value that determines whether a horizontal scroll indicator is
    * shown in the `WebView`. The default value is `true`.