Using regexp in org-refile-targets and the `:refile-targets` property in org-capture-templates

I am trying to specify a refile target with a regexp, but can't get it to work. Specifically, I'm trying to use the new :refile-targets property in org-capture-templates, but this question holds for using regexps in org-refile-targets as well.

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Since version 9.5, org mode comes with the :refile-targets org-capture-templates property. The description reads:

When exiting capture mode via org-capture-refile, the variable org-refile-targets will be temporarily bound to the value of this property.

In theory, org-refile-targets allows to set targets via regexp:

a cons cell (:regexp . "REGEXP") with a regular expression matching headlines that are refiling targets.

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I want to set :refile-targets to the parts of the current file indicated with <---:

* Undesirable heading ** Targets * Desirable heading ** Targets <---- this whole subtree is a desirable target ** Subheading *** Targets <---- this whole subtree is a desirable target 

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This is my capture template:

(("c" "Capture") ("ce" "Capture example") entry (file "path/to/file") "* %^{prompt}" :refile-targets REFILE_TARGET_DISCUSSED_BELOW) 

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These are representative examples of regexps that I have tried:

1. ((nil :regexp . "Targets")) obviously includes the undesirable Undesirable heading subtree
2. ((nil :regexp . "Desirable heading.*Targets")) does not return anything
3. ((nil :regexp . "Desirable heading\\.\\*Targets")) does not return anything

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Details:

• In org-refile-targets, the syntax is setq org-refile-targets '((nil :regexp . "REGEXP")), while in org-capture-templates the syntax is :refile-targets ((nil :regexp . "REGEXP")) (without the quote)
• The regexp in 3. was constructed with rx because the only example of complex :regexp in the wild that I have found used rx.