Explain that `configure_layout` URLs get embedded in iframes

[awaelchli]

🚀 Feature

Motivation

The user does not know what to do when an iframe can't display the contents.

Pitch

A) The frontend can display a useful message instead of a blank page

B) Add a sentence to the docs that says https links should be preferred over http. And that the source can still prevent that the content be embedded, which is out of our control (I assume).

Alternatives

Raise an error or emit a warning. This would lead to false positives, as we can't (?) know if the iframe or external site will allow the url or not. Or maybe we can know it in advance? In this case, we should warn on the Python side too.

Additional context

Discussed on Slack

cc @Borda @rohitgr7 @krishnakalyan3 @hhsecond @williamFalcon

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[awaelchli]

@alecmerdler You know this maybe: If such an error occurs, or the link is not accessible in the iframe, can our frontend display something helpful instead of the blank page? What are the best practices in your opinion here?

[alecmerdler]

@awaelchli I wish, we wanted to do something similar to show loading spinners. Unfortunately, modern browsers have strict security features that prevent the external page from accessing the contents of an <iframe> (except through very specific channels, which we use to pass the Lightning app state back and forth).

[williamFalcon]

yes, let’s show a warning @awaelchli. don’t rely on docs as the first line of usability. i’m ok with false warnings… i’d rather get a false warning than spend an hour trying to figure out what is wrong