From the Experience Manager overview in the docs regarding the Session-enabled Content Service:
The Session-enabled Content Service arranges session-specific interaction with the Content Data Store: only the user who is making updates sees this content while editing; other visitors of the staging Web site see the latest content that is checked in on the Content Manager side.
Makes sense, normal visitors to an XPM-enabled staging site should only see published content.
Is the same true if there are two editors making changes to the same page at the same time (say different component presentations on that page)?
Should Editor A be prompted to "Update preview" if a change is made in the page they're looking at in XPM, by Editor B (whose on a different machine/browser)? To clarify, Editor B hasn't clicked "Finish Editing", they've simply made a change and clicked out of the component presentation, triggering XPM to save the change.
The line in the quote above - only the user who is making updates sees this content while editing - suggests Editor A should not, their session isn't affected by Editor B's session.
Is that true because my tests show it isn't (Editor A is prompted to update their preview & see's changes by Editor B shortly after they make them) and I'm not sure if that's a bug or not!