MIT-licensed, open source, java-based Jsoup HTML parser can make it. To install Jsoup simply download the latest jar from https://jsoup.org/download then load it as a codeset using Designer Studio -> Application -> Distribution -> Import.
Then create a wrapper Function rule to use jsoup api, org.jsoup.nodes.Document.wholeText().
The pain point is that for certain properties (e.x. pxCreateOperator, pzInsKey, etc.) embedded in the correspondence rule, I have to switch to the <Source> mode editor and specify mode="normal" attribute.
Otherwise, there will be unexpected spaces and line breaks automatically appended around the property value.
All modifications made in the <Source> mode will be lost, if you switch back to Rich Text Editor mode. What a pity :-(