Regardings to the post https://community1.pega.com/community/product-support/question/want-know-if-there-elaborate-list-anywhere-which-tells-about-all#comment-form, I have found a way to fix the warning pxDisplayText on paragraph rules.

For this, you need to enable "Source" on the toolbar. Then just add format="pxDisplayText" in your Pega property tag.

Ex : <pega:reference format="pxDisplayText" name="aProperty"></pega:reference>

I hope this will help.