When will iframe content be indexed as part of the surrounding page?

Question

Our system provides a web front-end. A potential client would like to set up his own portal, and place our pages within his own pages, using iframes. He'd also like Google to index the joined content. I'm wondering if that's possible.

Note that since the client is going to own both his portal and ours, he can place both under the same domain. So the iframe will actually bringing content from the same website, and not from some unrelated source.

If this won't work, is there any alternative way to join content on the browser's end, in a way acceptable by search engines? Worst comes to worst he'd have to use our API and build the complete pages on his back end, but I'm looking for alternatives.

Answer 1

You're mashing concepts together in your question.
Even if the content of the iframe were indexed (I've seen a little evidence for this but can't definitively say one way or the other myself), it would–and should–not be considered part of the surrounding page and any ranking etc. for those portions would/should be assigned to the site the iframe comes from. The entire point of iframes is that they're external content.

What you're describing as "worst comes to worst" is what you should be doing in the first place. I suppose if the two domains will somehow live on the same server, you might get away with file-level includes or something, but that sounds potentially messy.