Lcp timing allow origin (#37743)

* Update LCP render time docs
* Update Element Timing too

files/en-us/web/api/largestcontentfulpaint/index.md

@@ -85,9 +85,13 @@ observer.observe({ type: "largest-contentful-paint", buffered: true });
 
 ### Cross-origin image render time
 
-For security reasons, the value of the {{domxref("LargestContentfulPaint.renderTime", "renderTime")}} property is `0` if the resource is a cross-origin request. Instead the {{domxref("LargestContentfulPaint.loadTime", "loadTime")}} is exposed. To expose cross-origin render time information, the {{HTTPHeader("Timing-Allow-Origin")}} HTTP response header needs to be set.
+For security reasons, the value of the {{domxref("LargestContentfulPaint.renderTime", "renderTime")}} property was originally `0` if the resource is a cross-origin request. Instead the {{domxref("LargestContentfulPaint.loadTime", "loadTime")}} property should be used as a fallback.
 
-For example, to allow `https://developer.mozilla.org` to see `renderTime`, the cross-origin resource should send:
+Browsers [may now expose a slightly coarsened render time](https://github.com/w3c/paint-timing/issues/104) in these situations. Check for [browser support](#browser_compatibility).
+
+To expose more accurate cross-origin render-time information, the {{HTTPHeader("Timing-Allow-Origin")}} HTTP response header needs to be set.
+
+For example, to allow `https://developer.mozilla.org` to see an accurate `renderTime`, the cross-origin resource should send:
 
 ```http
 Timing-Allow-Origin: https://developer.mozilla.org

files/en-us/web/api/largestcontentfulpaint/rendertime/index.md

@@ -34,9 +34,13 @@ observer.observe({ type: "largest-contentful-paint", buffered: true });
 
 ### Cross-origin image render time
 
-For security reasons, the value of the `renderTime` property is `0` if the resource is a cross-origin request. Instead the {{domxref("LargestContentfulPaint.loadTime", "loadTime")}} is exposed. To expose cross-origin render time information, the {{HTTPHeader("Timing-Allow-Origin")}} HTTP response header needs to be set.
+For security reasons, the value of the {{domxref("LargestContentfulPaint.renderTime", "renderTime")}} property was originally `0` if the resource is a cross-origin request. Instead the {{domxref("LargestContentfulPaint.loadTime", "loadTime")}} property should be used as a fallback.
 
-For example, to allow `https://developer.mozilla.org` to see `renderTime`, the cross-origin resource should send:
+Browsers [may now expose a slightly coarsened render time](https://github.com/w3c/paint-timing/issues/104) in threse situations. Check for [browser support](#browser_compatibility).
+
+To expose more accurate cross-origin render-time information, the {{HTTPHeader("Timing-Allow-Origin")}} HTTP response header needs to be set.
+
+For example, to allow `https://developer.mozilla.org` to see an accurate `renderTime`, the cross-origin resource should send:
 
 ```http
 Timing-Allow-Origin: https://developer.mozilla.org

files/en-us/web/api/performanceelementtiming/rendertime/index.md

@@ -47,9 +47,13 @@ observer.observe({ type: "element", buffered: true });
 
 ### Cross-origin image render time
 
-For security reasons, the value of the `renderTime` property is `0` if the resource is a cross-origin request. To expose cross-origin render time information, the {{HTTPHeader("Timing-Allow-Origin")}} HTTP response header needs to be set.
+For security reasons, the value of the `renderTime` property was originally `0` if the resource is a cross-origin request. Instead the `loadTime` property should be used as a fallback.
 
-For example, to allow `https://developer.mozilla.org` to see `renderTime`, the cross-origin resource should send:
+Browsers [may now expose a slightly coarsened render time](https://github.com/w3c/paint-timing/issues/104) in these situations. Check for [browser support](#browser_compatibility).
+
+To expose more accurate cross-origin render-time information, the {{HTTPHeader("Timing-Allow-Origin")}} HTTP response header needs to be set.
+
+For example, to allow `https://developer.mozilla.org` to see an accurate `renderTime`, the cross-origin resource should send:
 
 ```http
 Timing-Allow-Origin: https://developer.mozilla.org