Add comment explaining unusual return behavior of page.evaluate

packages/playwright/src/takeSnapshot.ts

@@ -35,6 +35,9 @@ async function takeSnapshot(
   // Serialize and capture the DOM
   const domSnapshot: elementNode = await page.evaluate(dedent`
     ${rrweb};
+    // page.evaluate returns the value of the function being evaluated. In this case, it means that
+    // it is returning either the resolved value of the Promise or the return value of the call to
+    // the snapshot function. See https://playwright.dev/docs/api/class-page#page-evaluate.
     if (typeof define === "function" && define.amd) {
       // AMD support is detected, so we need to load rrwebSnapshot asynchronously
       new Promise((resolve) => {