Anne van Kesteren wrote:
To ensure that naïve implementors don't overlook the potential issue
here. An implementation of NSResolver can be provided by the script
author as the specification explains and the script author can do all
kinds of weird things that don't match a conforming implementation of
NSResolver (such as mutating the DOM tree).
Is a conforming querySelector implementation allowed to throw an
exception when this happens?
No. It is only allowed to throw an exception when the text says so.
In that case, can you please describe what is a conforming behavior for a
querySelector (or querySelectorAll) implementation if:
1) It needs to call the NSResolver on every match attempt
2) The NSResolver mutates the DOM on every match attempt
Throwing an exception is not conformant. Is returning null from querySelector
conformant? Is returning a node that is not first in the document? Is
returning an empty list from querySelectorAll? Returning a list that's not in
document order? Returning a list in which a node is present twice?
If we read the spec literally, as you do here, the answers to all those are
"no".
If you're going to require the implementation to "deal" with NSResolvers which
do random stuff but put too many constraints on what it's allowed to do to deal
with them (as you are), you make an implementation impossible.
Now maybe you're actually requiring that the number of calls to the NSResolver
for any given selector and initial DOM tree is bounded in the face of all
possible mutations by the NSResolver and that hence the DOM will at some point
stabilize and it will be possible to return the things the spec requires be
returned. But if that's a constraint you want to place on implementations, you
should probably spell it out clearly.
Note that in Gecko I suspect the NSResolver would only be called during the
parsing of the selector, so we could in fact return the things the spec
requires... on the post-mutation DOM, not the pre-mutation one. It's not clear
to me from the spec whether this would be conformant.
-Boris
