In Visualforce mashups, what happens if the external content takes time to load?

In Visualforce mashups, the behavior regarding external content loading is designed to enhance user experience. When external content takes time to load, it typically results in the user having to wait until the content is fully loaded before they can interact with the Visualforce page. This is because Visualforce effectively integrates with external resources via an iframe or similar mechanism, which does not inherently allow for intermediate loading states within the parent page.

If the external content is heavy or slow to respond, this could lead to a perception of lag, but the user remains on the same page and is visually unaware of any progress until the external content is loaded completely. The user interaction is temporarily halted until the content appears, which is aligned with why option B is the correct choice in this context.

Other options suggest different behaviors that do not accurately reflect the way Visualforce handles external content loading. For instance, redirecting the user to another page or fetching data in the background does not align with the synchronous nature of the content load in a mashup. Similarly, progressive loading implies that parts of the content would display incrementally, which is not how Visualforce mashups operate with external resources. Therefore, the correct understanding of the load behavior reflects that the user must wait until all content is