What?

Closes #56465

Fix empty heading element when post_title is empty but get_the_title returns markup by checking for text content after stripping HTML tags.

Why?

The Post Title block was outputting empty heading elements when plugins or themes filter the_title to add markup around an empty post title. This creates invalid HTML with headings that contain no text content, which can cause accessibility issues and semantic problems.

The specific issue occurred when:

1. A post has an empty title
2. A plugin/theme filters the_title to wrap the empty title with HTML markup (e.g., <span class="p-name"></span>)
3. The Post Title block would output something like <h2><span class="p-name"></span></h2> - an empty heading

This was particularly problematic with plugins like wp-uf2 (Microformats) that add semantic markup to post titles.

How?

Updated the condition in render_block_core_post_title() to check not only if the title is empty, but also if the title has no text content after stripping HTML tags using strip_tags().

The fix changes:

if ( ! $title ) {
    return '';
}

To:

if ( ! $title || ! strip_tags( $title ) ) {
    return '';
}

This ensures that if the title contains only HTML markup without any actual text content, the heading element will not be rendered at all, maintaining the original intention of not outputting empty headings.

Testing Instructions

1. Create a new post without a title
2. Add a Query Loop block to a page with a Post Title block inside
3. Add the following code to your theme's functions.php or create a test plugin:

   add_filter(
       'the_title',
       function( $title ) {
           return '<strong>' . $title . '</strong>';
       }
   );

4. View the frontend page and inspect the HTML
5. Verify that no empty heading element is rendered for the post with no title

Alternatively, test with the wp-uf2 (Microformats) plugin:

1. Install and activate the wp-uf2 plugin
2. Follow steps 1-2 above
3. View the frontend and verify no empty <h2><a href="..."><span class="p-name"></span></a></h2> is rendered

Screenshots or screencast

Before

After