Thymeleaf 3.0: th:text works with an expression, but th:replace doesn't

[Mike Grabl-j]

Thymeleaf 3.0

Variable

From the controller I sent:

model.addAttribute("theme", "holmes");

html

<!--<p th:text="${'themes/' + theme + '/general/footer::footer(theme=' + theme +')'}">test</p>-->
<footer th:replace="${'themes/' + theme + '/general/footer::footer(theme=' + theme +')'}">Footer</footer>

Exception

org.thymeleaf.exceptions.TemplateInputException: Error resolving template [${'themes/' + theme + '/general/footer], template might not exist or might not be accessible by any of the configured Template Resolvers (template: "themes/holmes/posts/postList" - line 25, col 9)

Proof that the commented expression works


Problem
The commented out expression works. But the uncommented one blows up. To the best of my ability I understand that the compiler sees a string rather than an expression here.

Could you help me understand:

1. What the difference is between the commented and uncommented lines.

2. How to write the replacement expression correctly.