In reply to Phil Johnston.

A reusable block requires each instance to have identical content. I want to create a layout pattern in which I can change the content, but not rearrange it. But if I edit the pattern layout I would want the layout change to also change the existing instances of the pattern.

Imagine including a php-template file with get_template_part and setting heading, text and image attributes (for example). I could include that template file many times, displaying different content each time. And if I change the template file, the change will affect every instance where that template is used. That’s what I wished patterns could be.