diff --git a/Libraries/LibWeb/DOM/EventHandler.idl b/Libraries/LibWeb/DOM/EventHandler.idl
index d737a9fa3a6..c83dbda0f87 100644
--- a/Libraries/LibWeb/DOM/EventHandler.idl
+++ b/Libraries/LibWeb/DOM/EventHandler.idl
@@ -26,6 +26,7 @@ interface mixin GlobalEventHandlers {
     attribute EventHandler onchange;
     attribute EventHandler onclick;
     attribute EventHandler onclose;
+    attribute EventHandler oncommand;
     attribute EventHandler oncontextlost;
     attribute EventHandler oncontextmenu;
     attribute EventHandler oncontextrestored;
diff --git a/Libraries/LibWeb/HTML/AttributeNames.h b/Libraries/LibWeb/HTML/AttributeNames.h
index a868a9e2173..3e27c7d122d 100644
--- a/Libraries/LibWeb/HTML/AttributeNames.h
+++ b/Libraries/LibWeb/HTML/AttributeNames.h
@@ -151,6 +151,7 @@ namespace AttributeNames {
     __ENUMERATE_HTML_ATTRIBUTE(onchange, "onchange")                                     \
     __ENUMERATE_HTML_ATTRIBUTE(onclick, "onclick")                                       \
     __ENUMERATE_HTML_ATTRIBUTE(onclose, "onclose")                                       \
+    __ENUMERATE_HTML_ATTRIBUTE(oncommand, "oncommand")                                   \
     __ENUMERATE_HTML_ATTRIBUTE(oncontextlost, "oncontextlost")                           \
     __ENUMERATE_HTML_ATTRIBUTE(oncontextmenu, "oncontextmenu")                           \
     __ENUMERATE_HTML_ATTRIBUTE(oncontextrestored, "oncontextrestored")                   \
diff --git a/Libraries/LibWeb/HTML/EventNames.h b/Libraries/LibWeb/HTML/EventNames.h
index 3420db8c3c4..3515a1fd346 100644
--- a/Libraries/LibWeb/HTML/EventNames.h
+++ b/Libraries/LibWeb/HTML/EventNames.h
@@ -31,6 +31,7 @@ namespace Web::HTML::EventNames {
     __ENUMERATE_HTML_EVENT(change)                   \
     __ENUMERATE_HTML_EVENT(click)                    \
     __ENUMERATE_HTML_EVENT(close)                    \
+    __ENUMERATE_HTML_EVENT(command)                  \
     __ENUMERATE_HTML_EVENT(complete)                 \
     __ENUMERATE_HTML_EVENT(connect)                  \
     __ENUMERATE_HTML_EVENT(contextlost)              \
diff --git a/Libraries/LibWeb/HTML/GlobalEventHandlers.h b/Libraries/LibWeb/HTML/GlobalEventHandlers.h
index f06e2d115db..4962eeb019f 100644
--- a/Libraries/LibWeb/HTML/GlobalEventHandlers.h
+++ b/Libraries/LibWeb/HTML/GlobalEventHandlers.h
@@ -22,6 +22,7 @@
     E(onchange, HTML::EventNames::change)                                     \
     E(onclick, UIEvents::EventNames::click)                                   \
     E(onclose, HTML::EventNames::close)                                       \
+    E(oncommand, HTML::EventNames::command)                                   \
     E(oncontextlost, HTML::EventNames::contextlost)                           \
     E(oncontextmenu, HTML::EventNames::contextmenu)                           \
     E(oncontextrestored, HTML::EventNames::contextrestored)                   \
diff --git a/Libraries/LibWeb/HTML/HTMLButtonElement.cpp b/Libraries/LibWeb/HTML/HTMLButtonElement.cpp
index 6a89afa9d87..96b5b6809f3 100644
--- a/Libraries/LibWeb/HTML/HTMLButtonElement.cpp
+++ b/Libraries/LibWeb/HTML/HTMLButtonElement.cpp
@@ -7,8 +7,10 @@
 #include <LibWeb/Bindings/HTMLButtonElementPrototype.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/Event.h>
+#include <LibWeb/HTML/CommandEvent.h>
 #include <LibWeb/HTML/HTMLButtonElement.h>
 #include <LibWeb/HTML/HTMLFormElement.h>
+#include <LibWeb/Namespace.h>
 
 namespace Web::HTML {
 
@@ -153,12 +155,111 @@ void HTMLButtonElement::activation_behavior(DOM::Event const& event)
             return;
     }
 
-    // FIXME: 4. Let target be the result of running element's get the commandfor associated element.
-    // FIXME: 5. If target is not null:
-    //           ...
+    // 4. Let target be the result of running element's get the commandfor associated element.
+    //    AD-HOC: Target needs to be an HTML Element in the following steps.
+    GC::Ptr<HTMLElement> target = as_if<HTMLElement>(m_command_for_element.ptr());
+    if (!target) {
+        auto target_id = attribute(AttributeNames::commandfor);
+        if (target_id.has_value()) {
+            root().for_each_in_inclusive_subtree_of_type<HTMLElement>([&](auto& candidate) {
+                if (candidate.attribute(HTML::AttributeNames::id) == target_id.value()) {
+                    target = &candidate;
+                    return TraversalDecision::Break;
+                }
+                return TraversalDecision::Continue;
+            });
+        }
+    }
+
+    // 5. If target is not null:
+    if (target) {
+        // 1. Let command be element's command attribute.
+        auto command = this->command();
+
+        // 2. If command is in the Unknown state, then return.
+        if (command.is_empty()) {
+            return;
+        }
+
+        // 3. Let isPopover be true if target's popover attribute is not in the no popover state; otherwise false.
+        auto is_popover = target->popover().has_value();
+
+        // 4. If isPopover is false and command is not in the Custom state:
+        auto command_is_in_custom_state = command.starts_with_bytes("--"sv);
+        if (!is_popover && !command.starts_with_bytes("--"sv)) {
+            // 1. Assert: target's namespace is the HTML namespace.
+            VERIFY(target->namespace_uri() == Namespace::HTML);
+
+            // 2. If this standard does not define is valid invoker command steps for target's local name, then return.
+            // 3. Otherwise, if the result of running target's corresponding is valid invoker command steps given command is false, then return.
+            if (!target->is_valid_invoker_command(command))
+                return;
+        }
+
+        // 5. Let continue be the result of firing an event named command at target, using CommandEvent, with its command attribute initialized to command, its source attribute initialized to element, and its cancelable and composed attributes initialized to true.
+        // SPEC-NOTE: DOM standard issue #1328 tracks how to better standardize associated event data in a way which makes sense on Events. Currently an event attribute initialized to a value cannot also have a getter, and so an internal slot (or map of additional fields) is required to properly specify this.
+        CommandEventInit event_init {};
+        event_init.command = command;
+        event_init.source = this;
+        event_init.cancelable = true;
+        event_init.composed = true;
+
+        auto event = CommandEvent::create(realm(), HTML::EventNames::command, move(event_init));
+        event->set_is_trusted(true);
+        auto continue_ = target->dispatch_event(event);
+
+        // 6. If continue is false, then return.
+        if (!continue_)
+            return;
+
+        // 7. If target is not connected, then return.
+        if (!target->is_connected())
+            return;
+
+        // 8. If command is in the Custom state, then return.
+        if (command_is_in_custom_state)
+            return;
+
+        // AD-HOC: The parameters provided in the spec do not match the function signatures in the following steps.
+        //         The inconsistent parameters were therefore selected ad hoc.
+
+        // 9. If command is in the Hide Popover state:
+        if (command == "hide-popover") {
+            // 1. If the result of running check popover validity given target, true, false, and null is true, then run the hide popover algorithm given target, true, true, and false.
+            if (MUST(target->check_popover_validity(ExpectedToBeShowing::Yes, ThrowExceptions::No, nullptr, IgnoreDomState::No))) {
+                MUST(target->hide_popover(FocusPreviousElement::Yes, FireEvents::Yes, ThrowExceptions::No, IgnoreDomState::No));
+            }
+        }
+
+        // 10. Otherwise, if command is in the Toggle Popover state:
+        else if (command == "toggle-popover") {
+            // 1. If the result of running check popover validity given target, false, false, and null is true, then run the show popover algorithm given target, true, true, and false.
+            if (MUST(target->check_popover_validity(ExpectedToBeShowing::No, ThrowExceptions::No, nullptr, IgnoreDomState::No))) {
+                MUST(target->show_popover(ThrowExceptions::No, this));
+            }
+
+            // 2. Otheriwse, if the result of running check popover validity given target, true, false, and null is true, then run the hide popover algorithm given target, true, true, and false.
+            else if (MUST(target->check_popover_validity(ExpectedToBeShowing::Yes, ThrowExceptions::No, nullptr, IgnoreDomState::No))) {
+                MUST(target->hide_popover(FocusPreviousElement::Yes, FireEvents::Yes, ThrowExceptions::No, IgnoreDomState::No));
+            }
+        }
+
+        // 11. Otherwise, if command is in the Show Popover state:
+        else if (command == "show-popover") {
+            // 1. If the result of running check popover validity given target, false, false, and null is true, then run the show popover algorithm given target, true, true, and false.
+            if (MUST(target->check_popover_validity(ExpectedToBeShowing::No, ThrowExceptions::No, nullptr, IgnoreDomState::No))) {
+                MUST(target->show_popover(ThrowExceptions::No, this));
+            }
+        }
+
+        // 12. Otherwise, if this standard defines invoker command steps for target's local name, then run the corresponding invoker command steps given target, element and command.
+        else {
+            target->invoker_command_steps(*this, command);
+        }
+    }
 
     // 6. Otherwise, run the popover target attribute activation behavior given element and event's target.
-    if (event.target() && event.target()->is_dom_node())
+    else if (event.target() && event.target()->is_dom_node())
         PopoverInvokerElement::popover_target_activation_behaviour(*this, as<DOM::Node>(*event.target()));
 }
 
diff --git a/Libraries/LibWeb/HTML/HTMLDialogElement.cpp b/Libraries/LibWeb/HTML/HTMLDialogElement.cpp
index 01ac0867cf9..af4aa372b46 100644
--- a/Libraries/LibWeb/HTML/HTMLDialogElement.cpp
+++ b/Libraries/LibWeb/HTML/HTMLDialogElement.cpp
@@ -443,4 +443,39 @@ void HTMLDialogElement::set_is_modal(bool is_modal)
     invalidate_style(DOM::StyleInvalidationReason::NodeRemove);
 }
 
+// https://html.spec.whatwg.org/multipage/interactive-elements.html#the-dialog-element:is-valid-invoker-command-steps
+bool HTMLDialogElement::is_valid_invoker_command(String& command)
+{
+    // 1. If command is in the Close state or in the Show Modal state, then return true.
+    if (command == "close" || command == "show-modal")
+        return true;
+
+    // 2. Return false.
+    return false;
+}
+
+// https://html.spec.whatwg.org/multipage/interactive-elements.html#the-dialog-element:invoker-command-steps
+void HTMLDialogElement::invoker_command_steps(DOM::Element& invoker, String& command)
+{
+    // 1. If element is in the popover showing state, then return.
+    if (popover_visibility_state() == PopoverVisibilityState::Showing) {
+        return;
+    }
+
+    // 2. If command is in the Close state and element has an open attribute:
+    if (command == "close" && has_attribute(AttributeNames::open)) {
+        // 1. Let value be invoker's value.
+        //    FIXME: This assumes invoker is a button.
+        auto value = invoker.get_attribute(AttributeNames::value);
+
+        // 2. Close the dialog element with value.
+        close_the_dialog(value);
+    }
+
+    // 3. If command is the Show Modal state and element does not have an open attribute, then show a modal dialog given element.
+    if (command == "show-modal" && !has_attribute(AttributeNames::open)) {
+        MUST(show_a_modal_dialog(*this));
+    }
+}
+
 }
diff --git a/Libraries/LibWeb/HTML/HTMLDialogElement.h b/Libraries/LibWeb/HTML/HTMLDialogElement.h
index 02e471e980b..5a8a1b81013 100644
--- a/Libraries/LibWeb/HTML/HTMLDialogElement.h
+++ b/Libraries/LibWeb/HTML/HTMLDialogElement.h
@@ -39,6 +39,9 @@ public:
     bool is_modal() const { return m_is_modal; }
     void set_is_modal(bool);
 
+    bool is_valid_invoker_command(String&) override;
+    void invoker_command_steps(DOM::Element&, String&) override;
+
 private:
     HTMLDialogElement(DOM::Document&, DOM::QualifiedName);
 
diff --git a/Libraries/LibWeb/HTML/HTMLElement.h b/Libraries/LibWeb/HTML/HTMLElement.h
index 636f629d17b..acf935f0461 100644
--- a/Libraries/LibWeb/HTML/HTMLElement.h
+++ b/Libraries/LibWeb/HTML/HTMLElement.h
@@ -151,6 +151,9 @@ public:
 
     bool is_inert() const { return m_inert; }
 
+    virtual bool is_valid_invoker_command(String&) { return false; }
+    virtual void invoker_command_steps(DOM::Element&, String&) { }
+
 protected:
     HTMLElement(DOM::Document&, DOM::QualifiedName);
 
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/button-event-dispatch.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/button-event-dispatch.txt
new file mode 100644
index 00000000000..01e711453e2
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/button-event-dispatch.txt
@@ -0,0 +1,45 @@
+Harness status: OK
+
+Found 39 tests
+
+38 Pass
+1 Fail
+Pass	event dispatches on click with addEventListener
+Pass	event dispatches on click with oncommand property
+Pass	setting custom command property to --foo (must include dash) sets event command
+Pass	setting custom command attribute to --foo (must include dash) sets event command
+Pass	setting custom command property to --foo- (must include dash) sets event command
+Pass	setting custom command attribute to --foo- (must include dash) sets event command
+Pass	setting custom command property to --cAsE-cArRiEs (must include dash) sets event command
+Pass	setting custom command attribute to --cAsE-cArRiEs (must include dash) sets event command
+Pass	setting custom command property to -- (must include dash) sets event command
+Pass	setting custom command attribute to -- (must include dash) sets event command
+Pass	setting custom command property to --a- (must include dash) sets event command
+Pass	setting custom command attribute to --a- (must include dash) sets event command
+Pass	setting custom command property to --a-b (must include dash) sets event command
+Pass	setting custom command attribute to --a-b (must include dash) sets event command
+Pass	setting custom command property to --- (must include dash) sets event command
+Pass	setting custom command attribute to --- (must include dash) sets event command
+Pass	setting custom command property to --show-picker (must include dash) sets event command
+Pass	setting custom command attribute to --show-picker (must include dash) sets event command
+Pass	setting custom command property to -foo (no dash) did not dispatch an event
+Pass	setting custom command attribute to -foo (no dash) did not dispatch an event
+Pass	setting custom command property to -foo- (no dash) did not dispatch an event
+Pass	setting custom command attribute to -foo- (no dash) did not dispatch an event
+Pass	setting custom command property to foo-bar (no dash) did not dispatch an event
+Pass	setting custom command attribute to foo-bar (no dash) did not dispatch an event
+Pass	setting custom command property to -foo bar (no dash) did not dispatch an event
+Pass	setting custom command attribute to -foo bar (no dash) did not dispatch an event
+Pass	setting custom command property to —-emdash (no dash) did not dispatch an event
+Pass	setting custom command attribute to —-emdash (no dash) did not dispatch an event
+Pass	setting custom command property to hidedocument (no dash) did not dispatch an event
+Pass	setting custom command attribute to hidedocument (no dash) did not dispatch an event
+Pass	event does not dispatch if click:preventDefault is called
+Pass	event does not dispatch on input[type=button]
+Pass	event does not dispatch if invoker is disabled
+Pass	event does NOT dispatch if button is form associated, with implicit type
+Pass	event does NOT dispatch if button is form associated, with explicit type=invalid
+Pass	event dispatches if button is form associated, with explicit type=button
+Pass	event does NOT dispatch if button is form associated, with explicit type=submit
+Pass	event does NOT dispatch if button is form associated, with explicit type=reset
+Fail	event dispatches if invokee is non-HTML Element
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-dialog-behavior.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-dialog-behavior.txt
new file mode 100644
index 00000000000..1c9afd09d07
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-dialog-behavior.txt
@@ -0,0 +1,56 @@
+Harness status: OK
+
+Found 50 tests
+
+48 Pass
+2 Fail
+Pass	invoking (with command property as show-modal) closed dialog opens as modal
+Pass	invoking (with command property as show-modal) closed dialog with preventDefault is noop
+Pass	invoking (with command property as show-modal) while changing command still opens as modal
+Pass	invoking (with command attribute as show-modal) closed dialog opens as modal
+Pass	invoking (with command attribute as show-modal) closed dialog with preventDefault is noop
+Pass	invoking (with command attribute as show-modal) while changing command still opens as modal
+Pass	invoking (with command property as sHoW-mOdAl) closed dialog opens as modal
+Pass	invoking (with command property as sHoW-mOdAl) closed dialog with preventDefault is noop
+Pass	invoking (with command property as sHoW-mOdAl) while changing command still opens as modal
+Pass	invoking (with command attribute as sHoW-mOdAl) closed dialog opens as modal
+Pass	invoking (with command attribute as sHoW-mOdAl) closed dialog with preventDefault is noop
+Pass	invoking (with command attribute as sHoW-mOdAl) while changing command still opens as modal
+Pass	invoking to close (with command property as close) open dialog closes
+Pass	invoking to close (with command property as close) open dialog closes and sets returnValue
+Pass	invoking to close (with command property as close) open dialog with preventDefault is no-op
+Pass	invoking to close (with command property as close) open modal dialog with preventDefault is no-op
+Pass	invoking to close (with command property as close) open dialog while changing command still closes
+Pass	invoking to close (with command property as close) open modal dialog while changing command still closes
+Pass	invoking to close (with command attribute as close) open dialog closes
+Pass	invoking to close (with command attribute as close) open dialog closes and sets returnValue
+Pass	invoking to close (with command attribute as close) open dialog with preventDefault is no-op
+Pass	invoking to close (with command attribute as close) open modal dialog with preventDefault is no-op
+Pass	invoking to close (with command attribute as close) open dialog while changing command still closes
+Pass	invoking to close (with command attribute as close) open modal dialog while changing command still closes
+Pass	invoking to close (with command property as cLoSe) open dialog closes
+Pass	invoking to close (with command property as cLoSe) open dialog closes and sets returnValue
+Pass	invoking to close (with command property as cLoSe) open dialog with preventDefault is no-op
+Pass	invoking to close (with command property as cLoSe) open modal dialog with preventDefault is no-op
+Pass	invoking to close (with command property as cLoSe) open dialog while changing command still closes
+Pass	invoking to close (with command property as cLoSe) open modal dialog while changing command still closes
+Pass	invoking to close (with command attribute as cLoSe) open dialog closes
+Pass	invoking to close (with command attribute as cLoSe) open dialog closes and sets returnValue
+Pass	invoking to close (with command attribute as cLoSe) open dialog with preventDefault is no-op
+Pass	invoking to close (with command attribute as cLoSe) open modal dialog with preventDefault is no-op
+Pass	invoking to close (with command attribute as cLoSe) open dialog while changing command still closes
+Pass	invoking to close (with command attribute as cLoSe) open modal dialog while changing command still closes
+Pass	invoking (as show-modal) open dialog is noop
+Pass	invoking (as show-modal) open modal, while changing command still a no-op
+Pass	invoking (as show-modal) closed popover dialog opens as modal
+Pass	invoking (as close) already closed dialog is noop
+Pass	invoking (as show-modal) dialog as open popover=manual is noop
+Pass	invoking (as show-modal) dialog as open popover=auto is noop
+Pass	invoking (as close) dialog as open popover=manual is noop
+Pass	invoking (as close) dialog as open popover=auto is noop
+Pass	invoking (as show-modal) dialog that is removed is noop
+Fail	invoking (as show-modal) dialog from a detached invoker
+Pass	invoking (as show-modal) detached dialog from a detached invoker
+Fail	invoking (as close) dialog that is removed is noop
+Pass	invoking (as close) dialog from a detached invoker
+Pass	invoking (as close) detached dialog from a detached invoker
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-popover-behavior.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-popover-behavior.txt
new file mode 100644
index 00000000000..a2df3fa252b
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-popover-behavior.txt
@@ -0,0 +1,32 @@
+Harness status: OK
+
+Found 27 tests
+
+27 Pass
+Pass	changing command attribute inside invokeevent doesn't impact the invocation
+Pass	invoking (as toggle-popover) closed popover opens
+Pass	invoking (as toggle-popover) closed popover with preventDefault does not open
+Pass	invoking (as show-popover) closed popover opens
+Pass	invoking (as show-popover) closed popover with preventDefault does not open
+Pass	invoking (as tOgGlE-pOpOvEr) closed popover opens
+Pass	invoking (as tOgGlE-pOpOvEr) closed popover with preventDefault does not open
+Pass	invoking (as sHoW-pOpOvEr) closed popover opens
+Pass	invoking (as sHoW-pOpOvEr) closed popover with preventDefault does not open
+Pass	invoking (as toggle-popover) open popover closes
+Pass	invoking (as toggle-popover) open popover with preventDefault does not close
+Pass	invoking (as toggle-popover) from within open popover closes
+Pass	invoking (as toggle-popover) from within open popover with preventDefault does not close
+Pass	invoking (as hide-popover) open popover closes
+Pass	invoking (as hide-popover) open popover with preventDefault does not close
+Pass	invoking (as hide-popover) from within open popover closes
+Pass	invoking (as hide-popover) from within open popover with preventDefault does not close
+Pass	invoking (as tOgGlE-pOpOvEr) open popover closes
+Pass	invoking (as tOgGlE-pOpOvEr) open popover with preventDefault does not close
+Pass	invoking (as tOgGlE-pOpOvEr) from within open popover closes
+Pass	invoking (as tOgGlE-pOpOvEr) from within open popover with preventDefault does not close
+Pass	invoking (as hIdE-pOpOvEr) open popover closes
+Pass	invoking (as hIdE-pOpOvEr) open popover with preventDefault does not close
+Pass	invoking (as hIdE-pOpOvEr) from within open popover closes
+Pass	invoking (as hIdE-pOpOvEr) from within open popover with preventDefault does not close
+Pass	invoking (as show-popover) open popover is noop
+Pass	invoking (as hide-popover) closed popover is noop
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/button-event-dispatch.html b/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/button-event-dispatch.html
new file mode 100644
index 00000000000..2e64ed07af0
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/button-event-dispatch.html
@@ -0,0 +1,226 @@
+<!doctype html>
+<meta charset="utf-8" />
+<meta name="author" title="Keith Cirkel" href="mailto:wpt@keithcirkel.co.uk" />
+<meta name="timeout" content="long" />
+<link rel="help" href="https://open-ui.org/components/invokers.explainer/" />
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="resources/invoker-utils.js"></script>
+
+<div id="invokee"></div>
+<button id="invokerbutton" commandfor="invokee" command="--custom-command"></button>
+<input type="button" id="invalidbutton" commandfor="invokee" command="--custom-command">
+<form id="aform"></form>
+
+<script>
+  aform.addEventListener('submit', (e) => (e.preventDefault()));
+
+  function resetState() {
+    invokerbutton.setAttribute("commandfor", "invokee");
+    invokerbutton.setAttribute("command", "--custom-command");
+    invokerbutton.removeAttribute("disabled");
+    invokerbutton.removeAttribute("form");
+    invokerbutton.removeAttribute("type");
+  }
+
+  test(function (t) {
+    let event = null;
+    invokee.addEventListener("command", (e) => (event = e), { once: true });
+    invokerbutton.click();
+    assert_true(event instanceof CommandEvent, "event is CommandEvent");
+    assert_equals(event.type, "command", "type");
+    assert_equals(event.bubbles, false, "bubbles");
+    assert_equals(event.composed, true, "composed");
+    assert_equals(event.isTrusted, true, "isTrusted");
+    assert_equals(event.command, "--custom-command", "command");
+    assert_equals(event.target, invokee, "target");
+    assert_equals(event.source, invokerbutton, "source");
+  }, "event dispatches on click with addEventListener");
+
+  test(function (t) {
+    let event = null;
+    t.add_cleanup(() => {
+        invokee.oncommand = null;
+    });
+    invokee.oncommand = (e) => (event = e);
+    invokerbutton.click();
+    assert_true(event instanceof CommandEvent, "event is CommandEvent");
+    assert_equals(event.type, "command", "type");
+    assert_equals(event.bubbles, false, "bubbles");
+    assert_equals(event.composed, true, "composed");
+    assert_equals(event.isTrusted, true, "isTrusted");
+    assert_equals(event.command, "--custom-command", "command");
+    assert_equals(event.target, invokee, "target");
+    assert_equals(event.source, invokerbutton, "source");
+  }, "event dispatches on click with oncommand property");
+
+  // valid custom invokeactions
+  ["--foo", "--foo-", "--cAsE-cArRiEs", "--", "--a-", "--a-b", "---", "--show-picker"].forEach(
+    (command) => {
+      test(function (t) {
+        t.add_cleanup(resetState);
+        let event = null;
+        invokee.addEventListener("command", (e) => (event = e), { once: true });
+        invokerbutton.command = command;
+        invokerbutton.click();
+        assert_true(event instanceof CommandEvent, "event is CommandEvent");
+        assert_equals(event.type, "command", "type");
+        assert_equals(event.bubbles, false, "bubbles");
+        assert_equals(event.composed, true, "composed");
+        assert_equals(event.isTrusted, true, "isTrusted");
+        assert_equals(event.command, command, "command");
+        assert_equals(event.target, invokee, "target");
+        assert_equals(event.source, invokerbutton, "source");
+      }, `setting custom command property to ${command} (must include dash) sets event command`);
+
+      test(function (t) {
+        t.add_cleanup(resetState);
+        let event = null;
+        invokee.addEventListener("command", (e) => (event = e), { once: true });
+        invokerbutton.setAttribute("command", command);
+        invokerbutton.click();
+        assert_true(event instanceof CommandEvent, "event is CommandEvent");
+        assert_equals(event.type, "command", "type");
+        assert_equals(event.bubbles, false, "bubbles");
+        assert_equals(event.composed, true, "composed");
+        assert_equals(event.isTrusted, true, "isTrusted");
+        assert_equals(event.command, command, "command");
+        assert_equals(event.target, invokee, "target");
+        assert_equals(event.source, invokerbutton, "source");
+      }, `setting custom command attribute to ${command} (must include dash) sets event command`);
+    },
+  );
+
+  // invalid custom invokeactions
+  ["-foo", "-foo-", "foo-bar", "-foo bar", "—-emdash", "hidedocument"].forEach((command) => {
+    test(function (t) {
+      t.add_cleanup(resetState);
+      let event = null;
+      invokee.addEventListener("command", (e) => (event = e), { once: true });
+      invokerbutton.command = command;
+      invokerbutton.click();
+      assert_equals(event, null, "event should not have fired");
+    }, `setting custom command property to ${command} (no dash) did not dispatch an event`);
+
+    test(function (t) {
+      t.add_cleanup(resetState);
+      let event = null;
+      invokee.addEventListener("command", (e) => (event = e), { once: true });
+      invokerbutton.setAttribute("command", command);
+      invokerbutton.click();
+      assert_equals(event, null, "event should not have fired");
+    }, `setting custom command attribute to ${command} (no dash) did not dispatch an event`);
+  });
+
+  test(function (t) {
+    let called = false;
+    invokerbutton.addEventListener(
+      "click",
+      (event) => {
+        event.preventDefault();
+      },
+      { once: true },
+    );
+    invokee.addEventListener(
+      "command",
+      (event) => {
+        called = true;
+      },
+      { once: true },
+    );
+    invokerbutton.click();
+    assert_false(called, "event was not called");
+  }, "event does not dispatch if click:preventDefault is called");
+
+  test(function (t) {
+    let event = null;
+    invokee.addEventListener("command", (e) => (event = e), { once: true });
+    invalidbutton.click();
+    assert_equals(event, null, "command should not have fired");
+  }, "event does not dispatch on input[type=button]");
+
+  test(function (t) {
+    t.add_cleanup(resetState);
+    let called = false;
+    invokee.addEventListener("command", (e) => (called = true), { once: true });
+    invokerbutton.setAttribute("disabled", "");
+    invokerbutton.click();
+    assert_false(called, "event was not called");
+  }, "event does not dispatch if invoker is disabled");
+
+  test(function (t) {
+    t.add_cleanup(resetState);
+    let called = false;
+    invokee.addEventListener("command", (e) => (called = true), { once: true });
+    invokerbutton.setAttribute("form", "aform");
+    invokerbutton.removeAttribute("type");
+    invokerbutton.click();
+    assert_false(called, "event was not called");
+  }, "event does NOT dispatch if button is form associated, with implicit type");
+
+  test(function (t) {
+    t.add_cleanup(resetState);
+    let called = false;
+    invokee.addEventListener("command", (e) => (called = true), { once: true });
+    invokerbutton.setAttribute("form", "aform");
+    invokerbutton.setAttribute("type", "invalid");
+    invokerbutton.click();
+    assert_false(called, "event was not called");
+  }, "event does NOT dispatch if button is form associated, with explicit type=invalid");
+
+  test(function (t) {
+    t.add_cleanup(resetState);
+    let event;
+    invokee.addEventListener("command", (e) => (event = e), { once: true });
+    invokerbutton.setAttribute("form", "aform");
+    invokerbutton.setAttribute("type", "button");
+    invokerbutton.click();
+    assert_true(event instanceof CommandEvent, "event is CommandEvent");
+    assert_equals(event.type, "command", "type");
+    assert_equals(event.bubbles, false, "bubbles");
+    assert_equals(event.composed, true, "composed");
+    assert_equals(event.isTrusted, true, "isTrusted");
+    assert_equals(event.command, "--custom-command", "command");
+    assert_equals(event.target, invokee, "target");
+    assert_equals(event.source, invokerbutton, "source");
+  }, "event dispatches if button is form associated, with explicit type=button");
+
+  test(function (t) {
+    t.add_cleanup(resetState);
+    let called = false;
+    invokee.addEventListener("command", (e) => (called = true), { once: true });
+    invokerbutton.setAttribute("form", "aform");
+    invokerbutton.setAttribute("type", "submit");
+    invokerbutton.click();
+    assert_false(called, "event was not called");
+  }, "event does NOT dispatch if button is form associated, with explicit type=submit");
+
+  test(function (t) {
+    t.add_cleanup(resetState);
+    let called = false;
+    invokee.addEventListener("command", (e) => (called = true), { once: true });
+    invokerbutton.setAttribute("form", "aform");
+    invokerbutton.setAttribute("type", "reset");
+    invokerbutton.click();
+    assert_false(called, "event was called");
+  }, "event does NOT dispatch if button is form associated, with explicit type=reset");
+
+  test(function (t) {
+    svgInvokee = document.createElementNS("http://www.w3.org/2000/svg", "svg");
+    svgInvokee.setAttribute("id", "svg-invokee");
+    t.add_cleanup(resetState);
+    document.body.append(svgInvokee);
+    assert_false(svgInvokee instanceof HTMLElement);
+    assert_true(svgInvokee instanceof Element);
+    let event = null;
+    svgInvokee.addEventListener("command", (e) => (event = e), { once: true });
+    invokerbutton.setAttribute("commandfor", "svg-invokee");
+    invokerbutton.setAttribute("command", "--custom-command");
+    assert_equals(invokerbutton.commandForElement, svgInvokee);
+    invokerbutton.click();
+    assert_not_equals(event, null, "event was called");
+    assert_true(event instanceof CommandEvent, "event is CommandEvent");
+    assert_equals(event.source, invokerbutton, "event.invoker is set to right element");
+    assert_equals(event.target, svgInvokee, "event.target is set to right element");
+  }, "event dispatches if invokee is non-HTML Element");
+</script>
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-dialog-behavior.html b/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-dialog-behavior.html
new file mode 100644
index 00000000000..d6cc93a9f9e
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-dialog-behavior.html
@@ -0,0 +1,376 @@
+<!doctype html>
+<meta charset="utf-8" />
+<meta name="author" title="Keith Cirkel" href="mailto:wpt@keithcirkel.co.uk" />
+<meta name="timeout" content="long">
+<link rel="help" href="https://open-ui.org/components/invokers.explainer/" />
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="resources/invoker-utils.js"></script>
+
+<dialog id="invokee">
+  <button id="containedinvoker" commandfor="invokee" command="close"></button>
+</dialog>
+<button id="invokerbutton" commandfor="invokee" command="show-modal"></button>
+
+<script>
+  function resetState() {
+    invokee.close();
+    try { invokee.hidePopover(); } catch {}
+    invokee.removeAttribute("popover");
+    invokee.returnValue = '';
+    invokerbutton.setAttribute("command", "show-modal");
+    containedinvoker.setAttribute("command", "close");
+    containedinvoker.removeAttribute("value");
+  }
+
+  // opening a dialog
+
+  ["show-modal", /* test case sensitivity */ "sHoW-mOdAl"].forEach(
+    (command) => {
+      ["property", "attribute"].forEach((setType) => {
+        test(
+          function (t) {
+            t.add_cleanup(resetState);
+            assert_false(invokee.open, "invokee.open");
+            assert_false(invokee.matches(":modal"), "invokee :modal");
+            if (setType === "property") {
+              invokerbutton.command = command;
+            } else {
+              invokerbutton.setAttribute("command", command);
+            }
+            invokerbutton.click();
+            assert_true(invokee.open, "invokee.open");
+            assert_true(invokee.matches(":modal"), "invokee :modal");
+          },
+          `invoking (with command ${setType} as ${command}) closed dialog opens as modal`,
+        );
+
+        test(
+          function (t) {
+            t.add_cleanup(resetState);
+            assert_false(invokee.open, "invokee.open");
+            assert_false(invokee.matches(":modal"), "invokee :modal");
+            invokee.addEventListener("command", (e) => e.preventDefault(), {
+              once: true,
+            });
+            if (setType === "property") {
+              invokerbutton.command = command;
+            } else {
+              invokerbutton.setAttribute("command", command);
+            }
+            invokerbutton.click();
+            assert_false(invokee.open, "invokee.open");
+            assert_false(invokee.matches(":modal"), "invokee :modal");
+          },
+          `invoking (with command ${setType} as ${command}) closed dialog with preventDefault is noop`,
+        );
+
+        test(
+          function (t) {
+            t.add_cleanup(resetState);
+            assert_false(invokee.open, "invokee.open");
+            assert_false(invokee.matches(":modal"), "invokee :modal");
+            invokee.addEventListener(
+              "command",
+              (e) => {
+                invokerbutton.setAttribute("command", "close");
+              },
+              { once: true },
+            );
+            if (setType === "property") {
+              invokerbutton.command = command;
+            } else {
+              invokerbutton.setAttribute("command", command);
+            }
+            invokerbutton.click();
+            assert_true(invokee.open, "invokee.open");
+            assert_true(invokee.matches(":modal"), "invokee :modal");
+          },
+          `invoking (with command ${setType} as ${command}) while changing command still opens as modal`,
+        );
+      });
+    },
+  );
+
+  // closing an already open dialog
+
+  ["close", /* test case sensitivity */ "cLoSe"].forEach((command) => {
+    ["property", "attribute"].forEach((setType) => {
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.show();
+          assert_true(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+          if (setType === "property") {
+            containedinvoker.command = command;
+          } else {
+            containedinvoker.setAttribute("command", command);
+          }
+          containedinvoker.click();
+          assert_equals(invokee.returnValue, "");
+          assert_false(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking to close (with command ${setType} as ${command}) open dialog closes`,
+      );
+
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.show();
+          assert_true(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+          if (setType === "property") {
+            containedinvoker.command = command;
+          } else {
+            containedinvoker.setAttribute("command", command);
+          }
+          containedinvoker.setAttribute("value", "foo");
+          containedinvoker.click();
+          assert_equals(invokee.returnValue, "foo");
+          assert_false(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking to close (with command ${setType} as ${command}) open dialog closes and sets returnValue`,
+      );
+
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.show();
+          assert_true(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+          if (typeof command === "string") {
+            if (setType === "property") {
+              containedinvoker.command = command;
+            } else {
+              containedinvoker.setAttribute("command", command);
+            }
+          }
+          invokee.addEventListener("command", (e) => e.preventDefault(), {
+            once: true,
+          });
+          containedinvoker.click();
+          assert_true(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking to close (with command ${setType} as ${command}) open dialog with preventDefault is no-op`,
+      );
+
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.showModal();
+          assert_true(invokee.open, "invokee.open");
+          assert_true(invokee.matches(":modal"), "invokee :modal");
+          if (setType === "property") {
+            containedinvoker.command = command;
+          } else {
+            containedinvoker.setAttribute("command", command);
+          }
+          invokee.addEventListener("command", (e) => e.preventDefault(), {
+            once: true,
+          });
+          containedinvoker.click();
+          assert_true(invokee.open, "invokee.open");
+          assert_true(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking to close (with command ${setType} as ${command}) open modal dialog with preventDefault is no-op`,
+      );
+
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.show();
+          assert_true(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+          if (setType === "property") {
+            containedinvoker.command = command;
+          } else {
+            containedinvoker.setAttribute("command", command);
+          }
+          invokee.addEventListener(
+            "command",
+            (e) => {
+              containedinvoker.setAttribute("command", "show");
+            },
+            { once: true },
+          );
+          containedinvoker.click();
+          assert_false(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking to close (with command ${setType} as ${command}) open dialog while changing command still closes`,
+      );
+
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.showModal();
+          assert_true(invokee.open, "invokee.open");
+          assert_true(invokee.matches(":modal"), "invokee :modal");
+          if (setType === "property") {
+            containedinvoker.command = command;
+          } else {
+            containedinvoker.setAttribute("command", command);
+          }
+          invokee.addEventListener(
+            "command",
+            (e) => {
+              containedinvoker.setAttribute("command", "show");
+            },
+            { once: true },
+          );
+          containedinvoker.click();
+          assert_false(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking to close (with command ${setType} as ${command}) open modal dialog while changing command still closes`,
+      );
+    });
+  });
+
+  // show-modal explicit behaviours
+
+  promise_test(async function (t) {
+    t.add_cleanup(resetState);
+    containedinvoker.setAttribute("command", "show-Modal");
+    invokee.show();
+    assert_true(invokee.open, "invokee.open");
+    assert_false(invokee.matches(":modal"), "invokee :modal");
+    containedinvoker.click();
+    assert_true(invokee.open, "invokee.open");
+    assert_false(invokee.matches(":modal"), "invokee :modal");
+  }, "invoking (as show-modal) open dialog is noop");
+
+  promise_test(async function (t) {
+    t.add_cleanup(resetState);
+    containedinvoker.setAttribute("command", "show-modal");
+    invokee.showModal();
+    assert_true(invokee.open, "invokee.open");
+    assert_true(invokee.matches(":modal"), "invokee :modal");
+    invokee.addEventListener(
+      "command",
+      (e) => {
+        containedinvoker.setAttribute("command", "close");
+      },
+      { once: true },
+    );
+    invokerbutton.click();
+    assert_true(invokee.open, "invokee.open");
+    assert_true(invokee.matches(":modal"), "invokee :modal");
+  }, "invoking (as show-modal) open modal, while changing command still a no-op");
+
+  promise_test(async function (t) {
+    t.add_cleanup(resetState);
+    invokerbutton.setAttribute("command", "show-modal");
+    assert_false(invokee.open, "invokee.open");
+    assert_false(invokee.matches(":modal"), "invokee :modal");
+    invokee.setAttribute("popover", "auto");
+    invokerbutton.click();
+    assert_true(invokee.open, "invokee.open");
+    assert_true(invokee.matches(":modal"), "invokee :modal");
+  }, "invoking (as show-modal) closed popover dialog opens as modal");
+
+  // close explicit behaviours
+
+  promise_test(async function (t) {
+    t.add_cleanup(resetState);
+    invokerbutton.setAttribute("command", "close");
+    assert_false(invokee.open, "invokee.open");
+    assert_false(invokee.matches(":modal"), "invokee :modal");
+    containedinvoker.click();
+    assert_false(invokee.open, "invokee.open");
+    assert_false(invokee.matches(":modal"), "invokee :modal");
+  }, "invoking (as close) already closed dialog is noop");
+
+  // Open Popovers using Dialog actions
+  ["show-modal", "close"].forEach((command) => {
+    ["manual", "auto"].forEach((popoverState) => {
+      test(
+        function (t) {
+          t.add_cleanup(resetState);
+          invokee.setAttribute("popover", popoverState);
+          invokee.showPopover();
+          containedinvoker.setAttribute("command", command);
+          assert_true(
+            invokee.matches(":popover-open"),
+            "invokee :popover-open",
+          );
+          assert_false(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+          invokee.addEventListener("command", (e) => e.preventDefault(), {
+            once: true,
+          });
+          containedinvoker.click();
+          assert_true(
+            invokee.matches(":popover-open"),
+            "invokee :popover-open",
+          );
+          assert_false(invokee.open, "invokee.open");
+          assert_false(invokee.matches(":modal"), "invokee :modal");
+        },
+        `invoking (as ${command}) dialog as open popover=${popoverState} is noop`,
+      );
+    });
+  });
+
+  // Elements being disconnected during invoke steps
+  ["show-modal", "close"].forEach((command) => {
+    promise_test(
+      async function (t) {
+        t.add_cleanup(() => {
+          document.body.prepend(invokee);
+          resetState();
+        });
+        const invokee = document.querySelector("#invokee");
+        invokerbutton.setAttribute("command", command);
+        assert_false(invokee.open, "invokee.open");
+        assert_false(invokee.matches(":modal"), "invokee :modal");
+        invokee.addEventListener(
+          "command",
+          (e) => {
+            invokee.remove();
+          },
+          {
+            once: true,
+          },
+        );
+        invokerbutton.click();
+        assert_false(invokee.open, "invokee.open");
+        assert_false(invokee.matches(":modal"), "invokee :modal");
+      },
+      `invoking (as ${command}) dialog that is removed is noop`,
+    );
+
+    promise_test(
+      async function (t) {
+        const invokerbutton = document.createElement("button");
+        invokerbutton.commandForElement = invokee;
+        invokerbutton.setAttribute("command", command);
+        assert_false(invokee.open, "invokee.open");
+        assert_false(invokee.matches(":modal"), "invokee :modal");
+        invokerbutton.click();
+        assert_false(invokee.open, "invokee.open");
+        assert_false(invokee.matches(":modal"), "invokee :modal");
+      },
+      `invoking (as ${command}) dialog from a detached invoker`,
+    );
+
+    promise_test(
+      async function (t) {
+        const invokerbutton = document.createElement("button");
+        const invokee = document.createElement("dialog");
+        invokerbutton.commandForElementt = invokee;
+        invokerbutton.setAttribute("command", command);
+        assert_false(invokee.open, "invokee.open");
+        assert_false(invokee.matches(":modal"), "invokee :modal");
+        invokerbutton.click();
+        assert_false(invokee.open, "invokee.open");
+        assert_false(invokee.matches(":modal"), "invokee :modal");
+      },
+      `invoking (as ${command}) detached dialog from a detached invoker`,
+    );
+  });
+</script>
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-popover-behavior.html b/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-popover-behavior.html
new file mode 100644
index 00000000000..7fcceea2c7f
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/semantics/the-button-element/command-and-commandfor/on-popover-behavior.html
@@ -0,0 +1,152 @@
+<!doctype html>
+<meta charset="utf-8" />
+<meta name="author" title="Keith Cirkel" href="mailto:wpt@keithcirkel.co.uk" />
+<meta name="timeout" content="long" />
+<link rel="help" href="https://open-ui.org/components/invokers.explainer/" />
+<script src="../../../../resources/testharness.js"></script>
+<script src="../../../../resources/testharnessreport.js"></script>
+<script src="resources/invoker-utils.js"></script>
+
+<div id="invokee" popover>
+  <button id="containedinvoker" commandfor="invokee" command="hide-popover"></button>
+</div>
+<button id="invokerbutton" commandfor="invokee" command="toggle-popover"></button>
+
+<script>
+  function resetState() {
+    invokerbutton.setAttribute("commandfor", "invokee");
+    invokerbutton.setAttribute("command", "toggle-popover");
+    containedinvoker.setAttribute("commandfor", "invokee");
+    containedinvoker.setAttribute("command", "hide-popover");
+    try {
+      invokee.hidePopover();
+    } catch {}
+    invokee.setAttribute("popover", "");
+  }
+
+  promise_test(async function (t) {
+    assert_false(invokee.matches(":popover-open"));
+    invokee.addEventListener("command", (e) => { invokerbutton.setAttribute('command', 'hide-popover'); }, {
+      once: true,
+    });
+    invokerbutton.click();
+    t.add_cleanup(resetState);
+    assert_true(invokee.matches(":popover-open"));
+  }, "changing command attribute inside invokeevent doesn't impact the invocation");
+
+  // Open actions
+  [
+    "toggle-popover",
+    "show-popover",
+    /* test case sensitivity */
+    "tOgGlE-pOpOvEr",
+    "sHoW-pOpOvEr",
+  ].forEach((command) => {
+    test(
+      function (t) {
+        t.add_cleanup(resetState);
+        invokerbutton.command = command;
+        assert_false(invokee.matches(":popover-open"));
+        invokerbutton.click();
+        assert_true(invokee.matches(":popover-open"));
+      },
+      `invoking (as ${command}) closed popover opens`,
+    );
+
+    test(
+      function (t) {
+        t.add_cleanup(resetState);
+        invokerbutton.command = command;
+        assert_false(invokee.matches(":popover-open"));
+        invokee.addEventListener("command", (e) => e.preventDefault(), {
+          once: true,
+        });
+        invokerbutton.click();
+        assert_false(invokee.matches(":popover-open"));
+      },
+      `invoking (as ${command}) closed popover with preventDefault does not open`,
+    );
+  });
+
+  // Close actions
+  [
+    "toggle-popover",
+    "hide-popover",
+    /* test case sensitivity */
+    "tOgGlE-pOpOvEr",
+    "hIdE-pOpOvEr",
+  ].forEach((command) => {
+    test(
+      function (t) {
+        t.add_cleanup(resetState);
+        invokerbutton.command = command;
+        invokee.showPopover();
+        assert_true(invokee.matches(":popover-open"));
+        invokerbutton.click();
+        assert_false(invokee.matches(":popover-open"));
+      },
+      `invoking (as ${command}) open popover closes`,
+    );
+
+    test(
+      function (t) {
+        t.add_cleanup(resetState);
+        invokerbutton.command = command;
+        invokee.showPopover();
+        assert_true(invokee.matches(":popover-open"));
+        invokee.addEventListener("command", (e) => e.preventDefault(), {
+          once: true,
+        });
+        invokerbutton.click();
+        assert_true(invokee.matches(":popover-open"));
+      },
+      `invoking (as ${command}) open popover with preventDefault does not close`,
+    );
+
+    test(
+      function (t) {
+        t.add_cleanup(resetState);
+        containedinvoker.command = command;
+        invokee.showPopover();
+        assert_true(invokee.matches(":popover-open"));
+        containedinvoker.click();
+        assert_false(invokee.matches(":popover-open"));
+      },
+      `invoking (as ${command}) from within open popover closes`,
+    );
+
+    test(
+      function (t) {
+        t.add_cleanup(resetState);
+        containedinvoker.command = command;
+        invokee.showPopover();
+        invokee.addEventListener("command", (e) => e.preventDefault(), {
+          once: true,
+        });
+        assert_true(invokee.matches(":popover-open"));
+        containedinvoker.click();
+        assert_true(invokee.matches(":popover-open"));
+      },
+      `invoking (as ${command}) from within open popover with preventDefault does not close`,
+    );
+  });
+
+  // show-popover specific
+  test(function (t) {
+    t.add_cleanup(resetState);
+    invokerbutton.setAttribute("command", "show-popover");
+    invokee.showPopover();
+    assert_true(invokee.matches(":popover-open"));
+    invokerbutton.click();
+    assert_true(invokee.matches(":popover-open"));
+  }, "invoking (as show-popover) open popover is noop");
+
+  // hide-popover specific
+  test(function (t) {
+    t.add_cleanup(resetState);
+    invokerbutton.setAttribute("command", "hide-popover");
+    assert_false(invokee.matches(":popover-open"));
+    invokerbutton.click();
+    assert_false(invokee.matches(":popover-open"));
+  }, "invoking (as hide-popover) closed popover is noop");
+</script>