[whatwg] Sublties with seamless navigation

[Adam Barth]

Consider the following requirement for seamless iframes:

http://www.whatwg.org/specs/web-apps/current-work/#seamlessLinks

[[
If the source browsing context is the same as the browsing context
being navigated, and this browsing context has its seamless browsing
context flag set, and the browsing context being navigated was not
chosen using an explicit self-navigation override, then find the
nearest ancestor browsing context that does not have its seamless
browsing context flag set, and continue these steps as if that
browsing context was the one that was going to be navigated instead.
]]

However, that requirement seems to be a bit too agressive.  For
example, setting the "src" attribute on the iframe element loads the
document in the iframe using the Navigate keyword.  Should we be more
explicit in <http://www.whatwg.org/specs/web-apps/current-work/#dom-iframe-src>
about what the source browsing context is?  Is it always the browsing
context that contains the <iframe> element, or does it depend on which
script is manipulating the src attribute (e.g., via the DOM)?  Should
setting the src attribute use an explicit self-navigation override?

The easiest solution is probably to specify the source browsing
context explicitly, as we do for window.open
<http://www.whatwg.org/specs/web-apps/current-work/#dom-open> and
location.href <http://www.whatwg.org/specs/web-apps/current-work/#dom-location-href>.

Thanks!
Adam