diff --git a/testing/web-platform/tests/html/dom/elements/global-attributes/dir-assorted.window.js b/testing/web-platform/tests/html/dom/elements/global-attributes/dir-assorted.window.js
index 65a1a2e063bea..ee7e01fd128b6 100644
--- a/testing/web-platform/tests/html/dom/elements/global-attributes/dir-assorted.window.js
+++ b/testing/web-platform/tests/html/dom/elements/global-attributes/dir-assorted.window.js
@@ -289,3 +289,157 @@ direction
 "
 )
 ;
+test
+(
+(
+)
+=
+>
+{
+let
+container1
+=
+document
+.
+createElement
+(
+"
+div
+"
+)
+;
+document
+.
+body
+.
+appendChild
+(
+container1
+)
+;
+let
+container2
+=
+document
+.
+createElement
+(
+"
+div
+"
+)
+;
+for
+(
+let
+container
+of
+[
+container1
+container2
+]
+)
+{
+container
+.
+dir
+=
+"
+rtl
+"
+;
+let
+e
+=
+document
+.
+createElement
+(
+"
+div
+"
+)
+;
+assert_true
+(
+e
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+)
+;
+container
+.
+appendChild
+(
+e
+)
+;
+assert_false
+(
+e
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+)
+;
+e
+.
+remove
+(
+)
+;
+assert_true
+(
+e
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+)
+;
+}
+container1
+.
+remove
+(
+)
+;
+}
+"
+dir
+inheritance
+is
+correct
+after
+insertion
+and
+removal
+from
+document
+"
+)
+;
diff --git a/testing/web-platform/tests/html/dom/elements/global-attributes/dir-auto-dynamic-changes.window.js b/testing/web-platform/tests/html/dom/elements/global-attributes/dir-auto-dynamic-changes.window.js
new file mode 100644
index 0000000000000..14592bdfe9688
--- /dev/null
+++ b/testing/web-platform/tests/html/dom/elements/global-attributes/dir-auto-dynamic-changes.window.js
@@ -0,0 +1,1960 @@
+function
+setup_tree
+(
+light_tree
+shadow_tree
+)
+{
+let
+body
+=
+document
+.
+body
+;
+let
+old_length
+=
+body
+.
+childNodes
+.
+length
+;
+body
+.
+insertAdjacentHTML
+(
+"
+beforeend
+"
+light_tree
+.
+trim
+(
+)
+)
+;
+if
+(
+body
+.
+childNodes
+.
+length
+!
+=
+old_length
++
+1
+)
+{
+throw
+"
+unexpected
+markup
+"
+;
+}
+let
+result
+=
+body
+.
+lastChild
+;
+if
+(
+shadow_tree
+)
+{
+let
+shadow
+=
+result
+.
+querySelector
+(
+"
+#
+root
+"
+)
+.
+attachShadow
+(
+{
+mode
+:
+"
+open
+"
+}
+)
+;
+shadow
+.
+innerHTML
+=
+shadow_tree
+.
+trim
+(
+)
+;
+return
+[
+result
+shadow
+]
+;
+}
+return
+result
+;
+}
+test
+(
+t
+=
+>
+{
+let
+a
+=
+setup_tree
+(
+<
+div
+id
+=
+"
+a
+"
+dir
+=
+"
+auto
+"
+>
+<
+div
+id
+=
+"
+b
+"
+>
+<
+/
+div
+>
+hello
+<
+/
+div
+>
+)
+;
+let
+acs
+=
+getComputedStyle
+(
+a
+)
+;
+assert_true
+(
+a
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+:
+dir
+(
+ltr
+)
+matches
+before
+insertion
+"
+)
+;
+assert_false
+(
+a
+.
+matches
+(
+"
+:
+dir
+(
+rtl
+)
+"
+)
+"
+:
+dir
+(
+rtl
+)
+does
+not
+match
+before
+insertion
+"
+)
+;
+assert_equals
+(
+acs
+.
+direction
+"
+ltr
+"
+"
+CSSdirection
+before
+insertion
+"
+)
+;
+b
+.
+innerHTML
+=
+"
+\
+u05D0
+"
+;
+assert_false
+(
+a
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+:
+dir
+(
+ltr
+)
+does
+not
+match
+after
+insertion
+"
+)
+;
+assert_true
+(
+a
+.
+matches
+(
+"
+:
+dir
+(
+rtl
+)
+"
+)
+"
+:
+dir
+(
+rtl
+)
+matches
+after
+insertion
+"
+)
+;
+assert_equals
+(
+acs
+.
+direction
+"
+rtl
+"
+"
+CSSdirection
+after
+insertion
+"
+)
+;
+a
+.
+remove
+(
+)
+;
+}
+"
+dynamic
+insertion
+of
+RTL
+text
+in
+a
+child
+element
+"
+)
+;
+test
+(
+(
+)
+=
+>
+{
+let
+div_rtlchar
+=
+document
+.
+createElement
+(
+"
+div
+"
+)
+;
+div_rtlchar
+.
+innerHTML
+=
+"
+\
+u05D0
+"
+;
+let
+container1
+=
+document
+.
+createElement
+(
+"
+div
+"
+)
+;
+document
+.
+body
+.
+appendChild
+(
+container1
+)
+;
+let
+container2
+=
+document
+.
+createElement
+(
+"
+div
+"
+)
+;
+for
+(
+let
+container
+of
+[
+container1
+container2
+]
+)
+{
+container
+.
+dir
+=
+"
+auto
+"
+;
+assert_true
+(
+container
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+)
+;
+container
+.
+appendChild
+(
+div_rtlchar
+)
+;
+assert_false
+(
+container
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+)
+;
+div_rtlchar
+.
+remove
+(
+)
+;
+assert_true
+(
+container
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+)
+;
+}
+container1
+.
+remove
+(
+)
+;
+}
+"
+dir
+=
+auto
+changes
+for
+content
+insertion
+and
+removal
+in
+and
+out
+of
+document
+"
+)
+;
+test
+(
+(
+)
+=
+>
+{
+let
+tree
+shadow
+;
+[
+tree
+shadow
+]
+=
+setup_tree
+(
+<
+div
+>
+<
+div
+id
+=
+"
+root
+"
+>
+<
+span
+id
+=
+"
+l
+"
+>
+A
+<
+/
+span
+>
+<
+span
+id
+=
+"
+r
+"
+>
+\
+u05D0
+<
+/
+span
+>
+<
+/
+div
+>
+<
+/
+div
+>
+<
+slot
+id
+=
+"
+one
+"
+name
+=
+"
+one
+"
+dir
+=
+"
+auto
+"
+>
+\
+u05D0
+<
+/
+slot
+>
+<
+slot
+id
+=
+"
+two
+"
+dir
+=
+"
+auto
+"
+>
+<
+/
+slot
+>
+)
+;
+let
+one
+=
+shadow
+.
+getElementById
+(
+"
+one
+"
+)
+;
+let
+two
+=
+shadow
+.
+getElementById
+(
+"
+two
+"
+)
+;
+let
+l
+=
+tree
+.
+querySelector
+(
+"
+#
+l
+"
+)
+;
+let
+r
+=
+tree
+.
+querySelector
+(
+"
+#
+r
+"
+)
+;
+assert_false
+(
+one
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+one
+while
+empty
+"
+)
+;
+assert_true
+(
+two
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+two
+with
+both
+spans
+"
+)
+;
+l
+.
+slot
+=
+"
+one
+"
+;
+assert_true
+(
+one
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+one
+with
+LTR
+child
+span
+"
+)
+;
+assert_false
+(
+two
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+two
+with
+RTL
+child
+span
+"
+)
+;
+r
+.
+slot
+=
+"
+one
+"
+;
+assert_true
+(
+one
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+one
+with
+both
+child
+spans
+"
+)
+;
+assert_true
+(
+two
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+two
+while
+empty
+"
+)
+;
+l
+.
+slot
+=
+"
+"
+;
+assert_false
+(
+one
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+one
+with
+RTL
+child
+span
+"
+)
+;
+assert_true
+(
+two
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+#
+two
+with
+LTR
+child
+span
+"
+)
+;
+tree
+.
+remove
+(
+)
+;
+}
+"
+dir
+=
+auto
+changes
+for
+slot
+reassignment
+"
+)
+;
+test
+(
+(
+)
+=
+>
+{
+let
+tree
+shadow
+;
+[
+tree
+shadow
+]
+=
+setup_tree
+(
+<
+div
+dir
+=
+auto
+>
+<
+div
+id
+=
+root
+>
+<
+div
+id
+=
+text
+>
+A
+<
+/
+div
+>
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+dir
+=
+ltr
+>
+<
+slot
+id
+=
+slot
+dir
+=
+auto
+>
+<
+/
+slot
+>
+<
+/
+div
+>
+)
+;
+let
+text
+=
+tree
+.
+querySelector
+(
+"
+#
+text
+"
+)
+;
+let
+slot
+=
+shadow
+.
+querySelector
+(
+"
+#
+slot
+"
+)
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+before
+first
+text
+change
+"
+)
+;
+assert_true
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+before
+first
+text
+change
+"
+)
+;
+text
+.
+innerText
+=
+"
+\
+u05D0
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+after
+first
+text
+change
+"
+)
+;
+assert_false
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+after
+first
+text
+change
+"
+)
+;
+tree
+.
+dir
+=
+"
+rtl
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+before
+second
+text
+change
+"
+)
+;
+assert_false
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+before
+second
+text
+change
+"
+)
+;
+text
+.
+innerText
+=
+"
+A
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+after
+second
+text
+change
+"
+)
+;
+assert_true
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+after
+second
+text
+change
+"
+)
+;
+slot
+.
+dir
+=
+"
+ltr
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+before
+third
+text
+change
+"
+)
+;
+assert_true
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+before
+third
+text
+change
+"
+)
+;
+text
+.
+innerText
+=
+"
+\
+u05D0
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+after
+third
+text
+change
+"
+)
+;
+assert_true
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+after
+third
+text
+change
+"
+)
+;
+slot
+.
+dir
+=
+"
+auto
+"
+;
+tree
+.
+dir
+=
+"
+auto
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+after
+fourth
+text
+change
+"
+)
+;
+assert_false
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+after
+fourth
+text
+change
+"
+)
+;
+text
+.
+innerText
+=
+"
+A
+"
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+before
+fourth
+text
+change
+"
+)
+;
+assert_true
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+before
+fourth
+text
+change
+"
+)
+;
+slot
+.
+dir
+=
+"
+rtl
+"
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+before
+fifth
+text
+change
+"
+)
+;
+assert_false
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+before
+fifth
+text
+change
+"
+)
+;
+text
+.
+innerText
+=
+"
+\
+u05D0
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+node
+tree
+ancestor
+before
+fifth
+text
+change
+"
+)
+;
+assert_false
+(
+slot
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+slot
+before
+fifth
+text
+change
+"
+)
+;
+}
+"
+text
+changes
+affecting
+both
+slot
+and
+ancestor
+with
+dir
+=
+auto
+"
+)
+;
+test
+(
+(
+)
+=
+>
+{
+let
+tree
+=
+setup_tree
+(
+<
+div
+dir
+=
+"
+auto
+"
+>
+<
+span
+id
+=
+"
+a1
+"
+>
+A
+<
+/
+span
+>
+<
+span
+id
+=
+"
+aleph1
+"
+>
+\
+u05D0
+<
+/
+span
+>
+<
+span
+id
+=
+"
+a2
+"
+>
+A
+<
+/
+span
+>
+<
+span
+id
+=
+"
+aleph2
+"
+>
+\
+u05D0
+<
+/
+span
+>
+<
+/
+div
+>
+)
+;
+let
+a1
+=
+tree
+.
+querySelector
+(
+"
+#
+a1
+"
+)
+;
+let
+aleph1
+=
+tree
+.
+querySelector
+(
+"
+#
+aleph1
+"
+)
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+initial
+state
+"
+)
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+rtl
+)
+"
+)
+"
+initial
+state
+"
+)
+;
+a1
+.
+dir
+=
+"
+ltr
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+1
+"
+)
+;
+a1
+.
+dir
+=
+"
+invalid
+"
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+2
+"
+)
+;
+a1
+.
+dir
+=
+"
+rtl
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+3
+"
+)
+;
+a1
+.
+removeAttribute
+(
+"
+dir
+"
+)
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+4
+"
+)
+;
+a1
+.
+dir
+=
+"
+invalid
+"
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+5
+"
+)
+;
+a1
+.
+dir
+=
+"
+rtl
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+6
+"
+)
+;
+aleph1
+.
+dir
+=
+"
+auto
+"
+;
+assert_true
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+7
+"
+)
+;
+aleph1
+.
+dir
+=
+"
+invalid
+"
+;
+assert_false
+(
+tree
+.
+matches
+(
+"
+:
+dir
+(
+ltr
+)
+"
+)
+"
+after
+change
+8
+"
+)
+;
+}
+"
+dynamic
+changes
+to
+subtrees
+excluded
+as
+a
+result
+of
+the
+dir
+attribute
+"
+)
+;