I would like to (programmatically) highlight the dynamic values (context variables) of a thymeleaf template, by say wrapping each one of them in a span and applying a yellow background.
For example, this thymeleaf:

<div th:if="${a} == 'a'" th:text="'hello ' + ${a}?${b}:${c}">

executed with context:

{
  a: 'a',
  b: 'b',
  c: 'c',
}

should output:

<div>hello <span style="background-color: yellow;">b</span></div>

The surrounding span with the background is what I would like to have automatically inserted around every printed variable.

Changing the values themselves (to add the wrapping span) doesn't work because the values can be used in conditionals within the template, so changing values can alter what those conditionals evaluate to.

Search and replace can yield false postives because dynamic values can also organically occur in the template.

How can I achieve this?