' );
+
+ $p->next_tag( 'P' );
+ $this->assertSame( 'P', $p->get_tag(), "Expected to start test on P element but found {$p->get_tag()} instead." );
+ $this->assertSame( array( 'HTML', 'BODY', 'DIV', 'SPAN', 'P' ), $p->get_breadcrumbs(), 'Failed to produce expected DOM nesting.' );
+
+ $this->assertTrue( $p->next_tag(), 'Failed to advance past P tag to expected DIV opener.' );
+ $this->assertSame( 'DIV', $p->get_tag(), "Expected to find DIV element, but found {$p->get_tag()} instead." );
+ $this->assertSame( array( 'HTML', 'BODY', 'DIV', 'SPAN', 'DIV' ), $p->get_breadcrumbs(), 'Failed to produce expected DOM nesting: SPAN should still be open and DIV should be its child.' );
+ }
+
+ /*
+ * Verifies that when "in body" and encountering "any other end tag"
+ * that the HTML processor closes appropriate elements on the stack of
+ * open elements up to the matching opening.
+ *
+ * @ticket 58907
+ *
+ * @since 6.4.0
+ *
+ * @covers WP_HTML_Processor::step_in_body
+ */
+ public function test_in_body_any_other_end_tag_with_unclosed_non_special_element() {
+ $p = WP_HTML_Processor::createFragment( '
' );
+
+ $p->next_tag( 'CODE' );
+ $this->assertSame( 'CODE', $p->get_tag(), "Expected to start test on CODE element but found {$p->get_tag()} instead." );
+ $this->assertSame( array( 'HTML', 'BODY', 'DIV', 'SPAN', 'CODE' ), $p->get_breadcrumbs(), 'Failed to produce expected DOM nesting.' );
+
+ $this->assertTrue( $p->next_tag(), 'Failed to advance past CODE tag to expected SPAN closer.' );
+ $this->assertTrue( $p->is_tag_closer(), 'Expected to find closing SPAN, but found opener instead.' );
+ $this->assertSame( array( 'HTML', 'BODY', 'DIV' ), $p->get_breadcrumbs(), 'Failed to advance past CODE tag to expected DIV opener.' );
+
+ $this->assertTrue( $p->next_tag(), 'Failed to advance past SPAN closer to expected DIV opener.' );
+ $this->assertSame( 'DIV', $p->get_tag(), "Expected to find DIV element, but found {$p->get_tag()} instead." );
+ $this->assertSame( array( 'HTML', 'BODY', 'DIV', 'DIV' ), $p->get_breadcrumbs(), 'Failed to produce expected DOM nesting: SPAN should be closed and DIV should be its sibling.' );
+ }
+}
diff --git a/tests/phpunit/tests/html-api/wpHtmlSupportRequiredHtmlProcessor.php b/tests/phpunit/tests/html-api/wpHtmlSupportRequiredHtmlProcessor.php
new file mode 100644
index 0000000000..b9dbbc8cb8
--- /dev/null
+++ b/tests/phpunit/tests/html-api/wpHtmlSupportRequiredHtmlProcessor.php
@@ -0,0 +1,101 @@
+" );
+
+ $this->assertFalse( $p->step(), "Must support terminating elements in specific scope check before adding support for the {$tag_name} element." );
+ }
+
+ /**
+ * Generating implied end tags walks up the stack of open elements
+ * as long as any of the following missing elements is the current node.
+ *
+ * @since 6.4.0
+ *
+ * @ticket 58907
+ *
+ * @covers WP_HTML_Processor::generate_implied_end_tags
+ */
+ public function test_generate_implied_end_tags_needs_support() {
+ $this->ensure_support_is_added_everywhere( 'DD' );
+ $this->ensure_support_is_added_everywhere( 'DT' );
+ $this->ensure_support_is_added_everywhere( 'LI' );
+ $this->ensure_support_is_added_everywhere( 'OPTGROUP' );
+ $this->ensure_support_is_added_everywhere( 'OPTION' );
+ $this->ensure_support_is_added_everywhere( 'RB' );
+ $this->ensure_support_is_added_everywhere( 'RP' );
+ $this->ensure_support_is_added_everywhere( 'RT' );
+ $this->ensure_support_is_added_everywhere( 'RTC' );
+ }
+
+ /**
+ * Generating implied end tags thoroughly walks up the stack of open elements
+ * as long as any of the following missing elements is the current node.
+ *
+ * @since 6.4.0
+ *
+ * @ticket 58907
+ *
+ * @covers WP_HTML_Processor::generate_implied_end_tags_thoroughly
+ */
+ public function test_generate_implied_end_tags_thoroughly_needs_support() {
+ $this->ensure_support_is_added_everywhere( 'CAPTION' );
+ $this->ensure_support_is_added_everywhere( 'COLGROUP' );
+ $this->ensure_support_is_added_everywhere( 'DD' );
+ $this->ensure_support_is_added_everywhere( 'DT' );
+ $this->ensure_support_is_added_everywhere( 'LI' );
+ $this->ensure_support_is_added_everywhere( 'OPTGROUP' );
+ $this->ensure_support_is_added_everywhere( 'OPTION' );
+ $this->ensure_support_is_added_everywhere( 'RB' );
+ $this->ensure_support_is_added_everywhere( 'RP' );
+ $this->ensure_support_is_added_everywhere( 'RT' );
+ $this->ensure_support_is_added_everywhere( 'RTC' );
+ $this->ensure_support_is_added_everywhere( 'TBODY' );
+ $this->ensure_support_is_added_everywhere( 'TD' );
+ $this->ensure_support_is_added_everywhere( 'TFOOT' );
+ $this->ensure_support_is_added_everywhere( 'TH' );
+ $this->ensure_support_is_added_everywhere( 'HEAD' );
+ $this->ensure_support_is_added_everywhere( 'TR' );
+ }
+}