The original note was added in #267 and expanded in #347, but its advice is
impractical:
Sharing the activated sensors objects between multiple browsing
contexts/documents/windows means these Sensor objects could potentially be
shared by contexts in different top-level traversables (i.e. different
tabs).
Furthermore, if "can expose sensor readings" passes for one context but
not the other, "update sensor reading" would still invoke "report latest
reading updated" with sensors that cannot expose sensor readings.
Similarly, if the latest reading map is shared between multiple contexts,
an update would affect all contexts, including those for which "update
sensor reading" should not have been invoked in the first place (e.g. two
pages with the same origin share the latest readings map, but only one is
visible; updates to the latest reading map would be accessible from the
other as well).
PR #267 also made the "platform sensor" concept used in this section
per-browsing context (although in a very confusing way), which on its own is
a stricter requirement than what the note allowed, so we can drop the note
without making things less secure.
Incidentally, this also gets rid of one of the usages of "browsing context"
in the spec, which helps with #444.
The original note was added in #267 and expanded in #347, but its advice is impractical:
PR #267 also made the "platform sensor" concept used in this section per-browsing context (although in a very confusing way), which on its own is a stricter requirement than what the note allowed, so we can drop the note without making things less secure.
Incidentally, this also gets rid of one of the usages of "browsing context" in the spec, which helps with #444.
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