diff --git a/testing/web-platform/tests/dom/observable/tentative/observable-constructor.window.js b/testing/web-platform/tests/dom/observable/tentative/observable-constructor.window.js
index 42356b094c1f0..45e273b1b01b4 100644
--- a/testing/web-platform/tests/dom/observable/tentative/observable-constructor.window.js
+++ b/testing/web-platform/tests/dom/observable/tentative/observable-constructor.window.js
@@ -766,3 +766,244 @@ document
 "
 )
 ;
+promise_test
+(
+async
+t
+=
+>
+{
+/
+/
+Make
+this
+available
+off
+the
+global
+so
+the
+child
+can
+reach
+it
+.
+window
+.
+results
+=
+[
+]
+;
+const
+contentWin
+=
+await
+loadIframeAndReturnContentWindow
+(
+)
+;
+contentWin
+.
+eval
+(
+const
+parentResults
+=
+parent
+.
+results
+;
+const
+event_target
+=
+new
+EventTarget
+(
+)
+;
+/
+/
+Set
+up
+two
+event
+listeners
+both
+of
+which
+will
+mutate
+|
+parentResults
+|
+:
+/
+/
+1
+.
+A
+traditional
+event
+listener
+/
+/
+2
+.
+An
+observable
+event_target
+.
+addEventListener
+(
+'
+customevent
+'
+e
+=
+>
+parentResults
+.
+push
+(
+e
+)
+)
+;
+const
+source
+=
+event_target
+.
+on
+(
+'
+customevent
+'
+)
+;
+source
+.
+subscribe
+(
+e
+=
+>
+parentResults
+.
+push
+(
+e
+)
+)
+;
+/
+/
+Detach
+the
+iframe
+and
+fire
+an
+event
+at
+the
+event
+target
+.
+The
+parent
+will
+/
+/
+confirm
+that
+the
+observable
+'
+s
+next
+handler
+did
+not
+get
+invoked
+because
+/
+/
+the
+window
+is
+detached
+.
+const
+event
+=
+new
+Event
+(
+'
+customevent
+'
+)
+;
+window
+.
+frameElement
+.
+remove
+(
+)
+;
+parentResults
+.
+push
+(
+'
+detached
+'
+)
+;
+event_target
+.
+dispatchEvent
+(
+event
+)
+;
+)
+;
+assert_array_equals
+(
+results
+[
+"
+detached
+"
+]
+"
+Subscribe
+callback
+is
+never
+invoked
+"
+)
+;
+}
+"
+Observable
+from
+EventTarget
+does
+not
+get
+notified
+for
+events
+in
+detached
+documents
+"
+)
+;
diff --git a/testing/web-platform/tests/dom/observable/tentative/observable-event-target.any.js b/testing/web-platform/tests/dom/observable/tentative/observable-event-target.any.js
new file mode 100644
index 0000000000000..14c96bb475df7
--- /dev/null
+++ b/testing/web-platform/tests/dom/observable/tentative/observable-event-target.any.js
@@ -0,0 +1,551 @@
+test
+(
+(
+)
+=
+>
+{
+const
+target
+=
+new
+EventTarget
+(
+)
+;
+assert_implements
+(
+target
+.
+on
+"
+The
+EventTarget
+interface
+has
+an
+on
+method
+"
+)
+;
+assert_equals
+(
+typeof
+target
+.
+on
+"
+function
+"
+"
+EventTarget
+should
+have
+the
+on
+method
+"
+)
+;
+const
+testEvents
+=
+target
+.
+on
+(
+"
+test
+"
+)
+;
+assert_true
+(
+testEvents
+instanceof
+Observable
+"
+EventTarget
+.
+on
+returns
+an
+Observable
+"
+)
+;
+const
+results
+=
+[
+]
+;
+testEvents
+.
+subscribe
+(
+{
+next
+:
+value
+=
+>
+results
+.
+push
+(
+value
+)
+error
+:
+(
+)
+=
+>
+results
+.
+push
+(
+"
+error
+"
+)
+complete
+:
+(
+)
+=
+>
+results
+.
+push
+(
+"
+complete
+"
+)
+}
+)
+;
+assert_array_equals
+(
+results
+[
+]
+"
+Observable
+does
+not
+emit
+events
+until
+event
+is
+fired
+"
+)
+;
+const
+event
+=
+new
+Event
+(
+"
+test
+"
+)
+;
+target
+.
+dispatchEvent
+(
+event
+)
+;
+assert_array_equals
+(
+results
+[
+event
+]
+)
+;
+target
+.
+dispatchEvent
+(
+event
+)
+;
+assert_array_equals
+(
+results
+[
+event
+event
+]
+)
+;
+}
+"
+EventTarget
+.
+on
+(
+)
+returns
+an
+Observable
+"
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+target
+=
+new
+EventTarget
+(
+)
+;
+const
+testEvents
+=
+target
+.
+on
+(
+"
+test
+"
+)
+;
+const
+ac
+=
+new
+AbortController
+(
+)
+;
+const
+results
+=
+[
+]
+;
+testEvents
+.
+subscribe
+(
+{
+next
+:
+(
+value
+)
+=
+>
+results
+.
+push
+(
+value
+)
+error
+:
+(
+)
+=
+>
+results
+.
+push
+(
+'
+error
+'
+)
+complete
+:
+(
+)
+=
+>
+results
+.
+complete
+(
+'
+complete
+'
+)
+}
+{
+signal
+:
+ac
+.
+signal
+}
+)
+;
+assert_array_equals
+(
+results
+[
+]
+"
+Observable
+does
+not
+emit
+events
+until
+event
+is
+fired
+"
+)
+;
+const
+event1
+=
+new
+Event
+(
+"
+test
+"
+)
+;
+const
+event2
+=
+new
+Event
+(
+"
+test
+"
+)
+;
+const
+event3
+=
+new
+Event
+(
+"
+test
+"
+)
+;
+target
+.
+dispatchEvent
+(
+event1
+)
+;
+target
+.
+dispatchEvent
+(
+event2
+)
+;
+assert_array_equals
+(
+results
+[
+event1
+event2
+]
+)
+;
+ac
+.
+abort
+(
+)
+;
+target
+.
+dispatchEvent
+(
+event3
+)
+;
+assert_array_equals
+(
+results
+[
+event1
+event2
+]
+"
+Aborting
+the
+subscription
+removes
+the
+event
+listener
+and
+stops
+the
+"
++
+"
+emission
+of
+events
+"
+)
+;
+}
+"
+Aborting
+the
+subscription
+should
+stop
+the
+emission
+of
+events
+"
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+target
+=
+new
+EventTarget
+(
+)
+;
+const
+testEvents
+=
+target
+.
+on
+(
+"
+test
+"
+)
+;
+const
+results
+=
+[
+]
+;
+testEvents
+.
+subscribe
+(
+e
+=
+>
+results
+.
+push
+(
+e
+)
+)
+;
+testEvents
+.
+subscribe
+(
+e
+=
+>
+results
+.
+push
+(
+e
+)
+)
+;
+const
+event1
+=
+new
+Event
+(
+"
+test
+"
+)
+;
+const
+event2
+=
+new
+Event
+(
+"
+test
+"
+)
+;
+target
+.
+dispatchEvent
+(
+event1
+)
+;
+target
+.
+dispatchEvent
+(
+event2
+)
+;
+assert_array_equals
+(
+results
+[
+event1
+event1
+event2
+event2
+]
+)
+;
+}
+"
+EventTarget
+Observables
+can
+multicast
+subscriptions
+for
+event
+handling
+"
+)
+;
diff --git a/testing/web-platform/tests/trusted-types/trusted-types-event-handlers.html b/testing/web-platform/tests/trusted-types/trusted-types-event-handlers.html
index 96e167bd73070..5d185370c5d7e 100644
--- a/testing/web-platform/tests/trusted-types/trusted-types-event-handlers.html
+++ b/testing/web-platform/tests/trusted-types/trusted-types-event-handlers.html
@@ -268,6 +268,36 @@
 __proto__
 )
 {
+/
+/
+This
+captures
+all
+"
+on
+{
+foo
+}
+"
+handlers
+but
+not
+"
+on
+"
+itself
+which
+is
+an
+IDL
+/
+/
+attribute
+that
+returns
+an
+Observable
+.
 const
 should_be_event_handler
 =
@@ -279,6 +309,15 @@
 on
 "
 )
+&
+&
+name
+!
+=
+=
+"
+on
+"
 ;
 if
 (