diff --git a/src/wp-includes/html-api/class-wp-html-tag-processor.php b/src/wp-includes/html-api/class-wp-html-tag-processor.php
index 68c227f221066..91f192e9a5364 100644
--- a/src/wp-includes/html-api/class-wp-html-tag-processor.php
+++ b/src/wp-includes/html-api/class-wp-html-tag-processor.php
@@ -3978,8 +3978,7 @@ public function set_modifiable_text( string $plaintext_content ): bool {
 			self::STATE_COMMENT === $this->parser_state &&
 			self::COMMENT_AS_HTML_COMMENT === $this->comment_type
 		) {
-			// Check if the text could close the comment.
-			if ( 1 === preg_match( '/^-?>|--!?>/', $plaintext_content ) ) {
+			if ( self::has_comment_closer( $plaintext_content ) ) {
 				_doing_it_wrong(
 					__METHOD__,
 					__( 'Comment text cannot contain a comment closer.' ),
@@ -4093,14 +4092,13 @@ public function set_modifiable_text( string $plaintext_content ): bool {
 				 * start tag which follows `<!--` moves the tokenizer into the double-escaped
 				 * states, where a later `</script>` no longer closes the element.
 				 *
-				 * In both cases the tag name ends only at one of the characters matched
-				 * below, so text such as `</scriptx>` cannot change that structure and is
-				 * safe to set.
+				 * In both cases the tag name ends only at whitespace, "/" or ">", so text
+				 * such as `</scriptx>` cannot change that structure and is safe to set.
 				 *
 				 * @link https://html.spec.whatwg.org/#script-data-end-tag-name-state
 				 * @link https://html.spec.whatwg.org/#script-data-double-escape-start-state
 				 */
-				if ( 1 === preg_match( '~</?script[ \t\f\r\n/>]~i', $plaintext_content ) ) {
+				if ( array() !== self::find_tag_names( $plaintext_content, 'script', true ) ) {
 					_doing_it_wrong(
 						__METHOD__,
 						__( 'SCRIPT text with an unrecognized content type cannot contain a SCRIPT tag. Apply the escaping appropriate for the content type.' ),
@@ -4122,12 +4120,12 @@ public function set_modifiable_text( string $plaintext_content ): bool {
 				$tag_name = $this->get_tag();
 
 				/*
-				 * A tag name ends only at one of the characters matched below, so text
-				 * such as `</xmp-tag>` cannot close the element and is safe to set.
+				 * A tag name ends only at whitespace, "/" or ">", so text such as
+				 * `</xmp-tag>` cannot close the element and is safe to set.
 				 *
 				 * @link https://html.spec.whatwg.org/#rawtext-end-tag-name-state
 				 */
-				if ( 1 === preg_match( '~</' . preg_quote( $tag_name, '~' ) . '[ \t\f\r\n/>]~i', $plaintext_content ) ) {
+				if ( array() !== self::find_tag_names( $plaintext_content, $tag_name, false ) ) {
 					_doing_it_wrong(
 						__METHOD__,
 						sprintf(
@@ -4149,18 +4147,10 @@ public function set_modifiable_text( string $plaintext_content ): bool {
 				return true;
 
 			case 'STYLE':
-				$plaintext_content = preg_replace_callback(
-					'~</(?P<TAG_NAME>style)~i',
-					static function ( $tag_match ) {
-						return "\\3c\\2f{$tag_match['TAG_NAME']}";
-					},
-					$plaintext_content
-				);
-
 				$this->lexical_updates['modifiable text'] = new WP_HTML_Text_Replacement(
 					$this->text_starts_at,
 					$this->text_length,
-					$plaintext_content
+					self::escape_style_contents( $plaintext_content )
 				);
 
 				return true;
@@ -4516,53 +4506,145 @@ private function get_script_content_type(): ?string {
 	 * @return string Escaped form of input contents which will not lead to premature closing of the containing SCRIPT element.
 	 */
 	private static function escape_javascript_script_contents( string $sourcecode ): string {
-		$at      = 0;
-		$was_at  = 0;
-		$end     = strlen( $sourcecode );
 		$escaped = '';
+		$was_at  = 0;
 
 		/*
 		 * Replace all instances of the ASCII case-insensitive match of "<script"
 		 * and "</script", when followed by whitespace or "/" or ">", by using a
 		 * character replacement for the "s" (or the "S").
 		 */
-		while ( $at < $end ) {
-			$tag_at = strpos( $sourcecode, '<', $at );
-			if ( false === $tag_at ) {
-				break;
-			}
+		foreach ( self::find_tag_names( $sourcecode, 'script', true ) as $at ) {
+			$escaped .= substr( $sourcecode, $was_at, $at - $was_at );
+			$escaped .= 's' === $sourcecode[ $at ] ? '\u0073' : '\u0053';
+			$was_at   = $at + 1;
+		}
 
-			$tag_name_at       = $tag_at + 1;
-			$has_closing_slash = $tag_name_at < $end && '/' === $sourcecode[ $tag_name_at ];
-			$tag_name_at      += $has_closing_slash ? 1 : 0;
+		if ( 0 === $was_at ) {
+			return $sourcecode;
+		}
 
-			if ( 0 !== substr_compare( $sourcecode, 'script', $tag_name_at, 6, true ) ) {
-				$at = $tag_at + 1;
-				continue;
-			}
+		$escaped .= substr( $sourcecode, $was_at );
+		return $escaped;
+	}
 
-			if ( 1 !== strspn( $sourcecode, " \t\f\r\n/>", $tag_name_at + 6, 1 ) ) {
-				$at = $tag_name_at + 6;
-				continue;
+	/**
+	 * Indicates whether comment text holds a sequence which would end the comment.
+	 *
+	 * A comment ends at "-->" or "--!>", or at ">" or "->" right after "<!--".
+	 *
+	 * @link https://html.spec.whatwg.org/#comment-start-state
+	 *
+	 * @since 7.2.0
+	 * @ignore
+	 *
+	 * @param string $text Comment text.
+	 * @return bool Whether the text would end the comment.
+	 */
+	private static function has_comment_closer( string $text ): bool {
+		$at = 0;
+		while ( false !== ( $gt_at = strpos( $text, '>', $at ) ) ) {
+			$at = $gt_at + 1;
+			if (
+				0 === $gt_at ||
+				( 1 === $gt_at && '-' === $text[0] ) ||
+				( $gt_at >= 2 && '-' === $text[ $gt_at - 1 ] && '-' === $text[ $gt_at - 2 ] ) ||
+				( $gt_at >= 3 && '!' === $text[ $gt_at - 1 ] && '-' === $text[ $gt_at - 2 ] && '-' === $text[ $gt_at - 3 ] )
+			) {
+				return true;
 			}
-
-			$escaped .= substr( $sourcecode, $was_at, $tag_name_at - $was_at );
-			$escaped .= 's' === $sourcecode[ $tag_name_at ] ? '\u0073' : '\u0053';
-			$was_at   = $tag_name_at + 1;
-			$at       = $tag_name_at + 7;
 		}
 
-		if ( '' === $escaped ) {
-			return $sourcecode;
+		return false;
+	}
+
+	/**
+	 * Escape style tag contents.
+	 *
+	 * Prevent CSS text from modifying the HTML structure of a document and
+	 * ensure that it's contained within its enclosing STYLE tag as intended.
+	 *
+	 * @since 7.2.0
+	 * @ignore
+	 *
+	 * @param string $text Raw contents intended to be serialized into an HTML STYLE element.
+	 * @return string Escaped form of input contents which will not lead to premature closing of the containing STYLE element.
+	 */
+	private static function escape_style_contents( string $text ): string {
+		$escaped = '';
+		$was_at  = 0;
+
+		/*
+		 * Replace all instances of the ASCII case-insensitive match of "</style"
+		 * when followed by whitespace or "/" or ">", by using a CSS Unicode
+		 * escape sequence for the "s" (or the "S").
+		 *
+		 * CSS Unicode escape sequences will terminate at the first non-hexadecimal,
+		 * so the `t` character in `style` ensures that a Unicode escape sequence
+		 * like `\73t` is correctly interpreted as `st`.
+		 */
+		foreach ( self::find_tag_names( $text, 'style', false ) as $at ) {
+			$escaped .= substr( $text, $was_at, $at - $was_at );
+			$escaped .= 's' === $text[ $at ] ? '\73' : '\53';
+			$was_at   = $at + 1;
 		}
 
-		if ( $was_at < $end ) {
-			$escaped .= substr( $sourcecode, $was_at );
+		if ( 0 === $was_at ) {
+			return $text;
 		}
 
+		$escaped .= substr( $text, $was_at );
 		return $escaped;
 	}
 
+	/**
+	 * Finds each tag name in raw text which the tokenizer would read as a tag
+	 * of the given name.
+	 *
+	 * A tag name matches after "</", or also after "<" when start tags count,
+	 * in any mix of ASCII case, when whitespace, "/" or ">" follows it.
+	 *
+	 * Example:
+	 *
+	 *     array( 1, 10 ) === self::find_tag_names( '<script></SCRIPT/>', 'script', true );
+	 *     array( 10 )    === self::find_tag_names( '<script></SCRIPT/>', 'script', false );
+	 *     array()        === self::find_tag_names( '</scripts>', 'script', false );
+	 *
+	 * @since 7.2.0
+	 * @ignore
+	 *
+	 * @param string $text           Raw text.
+	 * @param string $tag_name       Tag name, in any case.
+	 * @param bool   $start_tags_too Whether a start tag matches as well as an end tag.
+	 * @return int[] Byte offset of the first letter of each matching tag name.
+	 */
+	private static function find_tag_names( string $text, string $tag_name, bool $start_tags_too ): array {
+		$found  = array();
+		$opener = $start_tags_too ? '<' : '</';
+		$length = strlen( $tag_name );
+		$end    = strlen( $text );
+		$at     = 0;
+
+		while ( false !== ( $tag_at = strpos( $text, $opener, $at ) ) ) {
+			$at = $tag_at + strlen( $opener );
+			if ( $start_tags_too && $at < $end && '/' === $text[ $at ] ) {
+				++$at;
+			}
+
+			// Tag names match ASCII case-insensitively. The first letter is compared before the name is copied.
+			if (
+				$at < $end &&
+				0 === strncasecmp( $text[ $at ], $tag_name, 1 ) &&
+				0 === strncasecmp( substr( $text, $at, $length ), $tag_name, $length ) &&
+				1 === strspn( $text, " \t\f\r\n/>", $at + $length, 1 )
+			) {
+				$found[] = $at;
+			}
+		}
+
+		return $found;
+	}
+
 	/**
 	 * Updates or creates a new attribute on the currently matched tag with the passed value.
 	 *
diff --git a/tests/phpunit/tests/customize/custom-css-setting.php b/tests/phpunit/tests/customize/custom-css-setting.php
index 06f77075d0ba8..e89adc95eba3c 100644
--- a/tests/phpunit/tests/customize/custom-css-setting.php
+++ b/tests/phpunit/tests/customize/custom-css-setting.php
@@ -392,7 +392,7 @@ public function test_wp_custom_css_cb_escapes_dangerous_html() {
 		$expected =
 			<<<'HTML'
 			<style id="wp-custom-css">
-			*::before { content: "\3c\2fstyle><script>alert(1)</script>"; }
+			*::before { content: "</\73tyle><script>alert(1)</script>"; }
 			</style>
 
 			HTML;
diff --git a/tests/phpunit/tests/html-api/wpHtmlTagProcessorModifiableText.php b/tests/phpunit/tests/html-api/wpHtmlTagProcessorModifiableText.php
index cd844a8cee326..1533d87b483e5 100644
--- a/tests/phpunit/tests/html-api/wpHtmlTagProcessorModifiableText.php
+++ b/tests/phpunit/tests/html-api/wpHtmlTagProcessorModifiableText.php
@@ -429,24 +429,30 @@ public function test_updates_basic_modifiable_text_on_supported_nodes( string $h
 	 */
 	public static function data_tokens_with_basic_modifiable_text_updates() {
 		return array(
-			'Text node (start)'       => array( 'Text', 1, 'Blubber', 'Blubber' ),
-			'Text node (middle)'      => array( '<em>Bold move</em>', 2, 'yo', '<em>yo</em>' ),
-			'PI node'                 => array( 'before<?wp-bit data?>after', 2, 'other', 'before<?wp-bit other?>after' ),
-			'PI node (no separator)'  => array( '<?wp-bit?>', 1, '{"just": "kidding"}', '<?wp-bit {"just": "kidding"}?>' ),
-			'Text node (end)'         => array( '<img>of a dog', 2, 'of a cat', '<img>of a cat' ),
-			'Encoded text node'       => array( '<figcaption>birds and dogs</figcaption>', 2, '<birds> & <dogs>', '<figcaption>&lt;birds&gt; &amp; &lt;dogs&gt;</figcaption>' ),
-			'IFRAME tag'              => array( 'before<iframe>old content</iframe>after', 2, '<p>raw & text</p>', 'before<iframe><p>raw & text</p></iframe>after' ),
-			'NOEMBED tag'             => array( 'before<noembed>old content</noembed>after', 2, '<p>raw & text</p>', 'before<noembed><p>raw & text</p></noembed>after' ),
-			'NOFRAMES tag'            => array( 'before<noframes>old content</noframes>after', 2, '<p>raw & text</p>', 'before<noframes><p>raw & text</p></noframes>after' ),
-			'XMP tag'                 => array( 'before<xmp>old content</xmp>after', 2, '<p>raw & text</p>', 'before<xmp><p>raw & text</p></xmp>after' ),
-			'SCRIPT tag'              => array( 'before<script></script>after', 2, 'const img = "<img> & <br>";', 'before<script>const img = "<img> & <br>";</script>after' ),
-			'STYLE tag'               => array( '<style></style>', 1, 'p::before { content: "<img> & </style>"; }', '<style>p::before { content: "<img> & \3c\2fstyle>"; }</style>' ),
-			'TEXTAREA tag'            => array( 'a<textarea>has no need to escape</textarea>b', 2, "so it <doesn't>", "a<textarea>so it <doesn't></textarea>b" ),
-			'TEXTAREA (escape)'       => array( 'a<textarea>has no need to escape</textarea>b', 2, 'but it does for </textarea>', 'a<textarea>but it does for &lt;/textarea></textarea>b' ),
-			'TEXTAREA (escape+attrs)' => array( 'a<textarea>has no need to escape</textarea>b', 2, 'but it does for </textarea not an="attribute">', 'a<textarea>but it does for &lt;/textarea not an="attribute"></textarea>b' ),
-			'TITLE tag'               => array( 'a<title>has no need to escape</title>b', 2, "so it <doesn't>", "a<title>so it <doesn't></title>b" ),
-			'TITLE (escape)'          => array( 'a<title>has no need to escape</title>b', 2, 'but it does for </title>', 'a<title>but it does for &lt;/title></title>b' ),
-			'TITLE (escape+attrs)'    => array( 'a<title>has no need to escape</title>b', 2, 'but it does for </title not an="attribute">', 'a<title>but it does for &lt;/title not an="attribute"></title>b' ),
+			'Text node (start)'               => array( 'Text', 1, 'Blubber', 'Blubber' ),
+			'Text node (middle)'              => array( '<em>Bold move</em>', 2, 'yo', '<em>yo</em>' ),
+			'PI node'                         => array( 'before<?wp-bit data?>after', 2, 'other', 'before<?wp-bit other?>after' ),
+			'PI node (no separator)'          => array( '<?wp-bit?>', 1, '{"just": "kidding"}', '<?wp-bit {"just": "kidding"}?>' ),
+			'Text node (end)'                 => array( '<img>of a dog', 2, 'of a cat', '<img>of a cat' ),
+			'Encoded text node'               => array( '<figcaption>birds and dogs</figcaption>', 2, '<birds> & <dogs>', '<figcaption>&lt;birds&gt; &amp; &lt;dogs&gt;</figcaption>' ),
+			'IFRAME tag'                      => array( 'before<iframe>old content</iframe>after', 2, '<p>raw & text</p>', 'before<iframe><p>raw & text</p></iframe>after' ),
+			'NOEMBED tag'                     => array( 'before<noembed>old content</noembed>after', 2, '<p>raw & text</p>', 'before<noembed><p>raw & text</p></noembed>after' ),
+			'NOFRAMES tag'                    => array( 'before<noframes>old content</noframes>after', 2, '<p>raw & text</p>', 'before<noframes><p>raw & text</p></noframes>after' ),
+			'XMP tag'                         => array( 'before<xmp>old content</xmp>after', 2, '<p>raw & text</p>', 'before<xmp><p>raw & text</p></xmp>after' ),
+			'SCRIPT tag'                      => array( 'before<script></script>after', 2, 'const img = "<img> & <br>";', 'before<script>const img = "<img> & <br>";</script>after' ),
+			'STYLE tag'                       => array( '<style></style>', 1, 'p::before { content: "<img> & </style>"; }', '<style>p::before { content: "<img> & </\73tyle>"; }</style>' ),
+			'STYLE tag (mixed casing)'        => array( '<style></style>', 1, 'p::before { content: "<img> & </StYlE>"; }', '<style>p::before { content: "<img> & </\53tYlE>"; }</style>' ),
+			'STYLE tag (trailing characters)' => array( '<style></style>', 1, "p::before { content: \"<img> & </style\t>\"; }", "<style>p::before { content: \"<img> & </\\73tyle\t>\"; }</style>" ),
+			'STYLE tag (non-closing tag)'     => array( '<style></style>', 1, 'p::before { content: "<img> & </stylesheet>"; }', '<style>p::before { content: "<img> & </stylesheet>"; }</style>' ),
+			'STYLE tag (repeats)'             => array( '<style></style>', 1, '*{ content: "</style></STYLE></style</style>" }', '<style>*{ content: "</\73tyle></\53TYLE></style</\73tyle>" }</style>' ),
+			'STYLE tag (terminators)'         => array( '<style></style>', 1, "*{ content: \"</style </style\f</style\r</style\n</style/\" }", "<style>*{ content: \"</\\73tyle </\\73tyle\f</\\73tyle\r</\\73tyle\n</\\73tyle/\" }</style>" ),
+			'STYLE tag (start tag)'           => array( '<style></style>', 1, '*{ content: "<style><STYLE>" }', '<style>*{ content: "<style><STYLE>" }</style>' ),
+			'TEXTAREA tag'                    => array( 'a<textarea>has no need to escape</textarea>b', 2, "so it <doesn't>", "a<textarea>so it <doesn't></textarea>b" ),
+			'TEXTAREA (escape)'               => array( 'a<textarea>has no need to escape</textarea>b', 2, 'but it does for </textarea>', 'a<textarea>but it does for &lt;/textarea></textarea>b' ),
+			'TEXTAREA (escape+attrs)'         => array( 'a<textarea>has no need to escape</textarea>b', 2, 'but it does for </textarea not an="attribute">', 'a<textarea>but it does for &lt;/textarea not an="attribute"></textarea>b' ),
+			'TITLE tag'                       => array( 'a<title>has no need to escape</title>b', 2, "so it <doesn't>", "a<title>so it <doesn't></title>b" ),
+			'TITLE (escape)'                  => array( 'a<title>has no need to escape</title>b', 2, 'but it does for </title>', 'a<title>but it does for &lt;/title></title>b' ),
+			'TITLE (escape+attrs)'            => array( 'a<title>has no need to escape</title>b', 2, 'but it does for </title not an="attribute">', 'a<title>but it does for &lt;/title not an="attribute"></title>b' ),
 		);
 	}
 
@@ -703,6 +709,8 @@ public static function data_unallowed_modifiable_text_updates() {
 		return array(
 			'Comment with -->'                        => array( '<!-- this is a comment -->', 'Comments end in -->' ),
 			'Comment with --!>'                       => array( '<!-- this is a comment -->', 'Invalid but legitimate comments end in --!>' ),
+			'Comment starting with >'                 => array( '<!-- this is a comment -->', '> ends an empty comment' ),
+			'Comment starting with ->'                => array( '<!-- this is a comment -->', '-> ends an empty comment' ),
 			'IFRAME with </iframe>'                   => array( '<iframe>Replace me</iframe>', 'Just a </iframe>' ),
 			'NOEMBED with </NOEMBED>'                 => array( '<noembed>Replace me</noembed>', 'Just a </NOEMBED>' ),
 			'NOFRAMES with </noframes attributes>'    => array( '<noframes>Replace me</noframes>', 'before</noframes sneaky>after' ),
@@ -721,6 +729,46 @@ public static function data_unallowed_modifiable_text_updates() {
 		);
 	}
 
+	/**
+	 * Ensures that comment text which resembles a comment closer, but cannot
+	 * end the comment, is allowed.
+	 *
+	 * @dataProvider data_comment_text_resembling_a_closer
+	 *
+	 * @param string $update Text resembling, but not forming, a comment closer.
+	 */
+	public function test_allows_comment_text_which_cannot_close_the_comment( string $update ): void {
+		$processor = new WP_HTML_Tag_Processor( '<!-- comment -->' );
+		$processor->next_token();
+
+		$this->assertTrue(
+			$processor->set_modifiable_text( $update ),
+			'Should have allowed text which cannot close the comment.'
+		);
+
+		$this->assertSame(
+			"<!--{$update}-->",
+			$processor->get_updated_html(),
+			'Should have updated the comment.'
+		);
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public static function data_comment_text_resembling_a_closer(): array {
+		return array(
+			'> after text'      => array( 'a>' ),
+			'-> after text'     => array( 'a->' ),
+			'-!> at the start'  => array( '-!>' ),
+			'--! before text'   => array( '--!x>' ),
+			'Spaced dashes'     => array( '- ->' ),
+			'Dashes at the end' => array( 'a--' ),
+		);
+	}
+
 	/**
 	 * Ensures that raw text which resembles a closing tag, but cannot close its
 	 * element, is allowed as modifiable text.
@@ -814,6 +862,7 @@ public static function data_script_tag_text_updates(): array {
 			'Tricky script open tag with \r\n'      => array( '<script></script>', "<!-- <script\r\n>", "<script><!-- <\\u0073cript\r\n></script>" ),
 			'Tricky script close tag with \r'       => array( '<script></script>', "// </script\r>", "<script>// </\\u0073cript\r></script>" ),
 			'Tricky script close tag with \r\n'     => array( '<script></script>', "// </script\r\n>", "<script>// </\\u0073cript\r\n></script>" ),
+			'Tag name terminators'                  => array( '<script></script>', "a<script b</script\tc<script\fd</script\ne<script/f", "<script>a<\\u0073cript b</\\u0073cript\tc<\\u0073cript\fd</\\u0073cript\ne<\\u0073cript/f</script>" ),
 			'Module tag'                            => array( '<script type="module"></script>', '"<script>"', '<script type="module">"<\u0073cript>"</script>' ),
 			'Tag with type'                         => array( '<script type="text/javascript"></script>', '"<script>"', '<script type="text/javascript">"<\u0073cript>"</script>' ),
 			'Tag with language'                     => array( '<script language="javascript"></script>', '"<script>"', '<script language="javascript">"<\u0073cript>"</script>' ),