> This split to XML also allowed us to implement a live UI reloading. It’s something that will save quite a lot of development time as you can see every change in the UI without recompilation and redeployment.

It looks like the Reactant UI is an add-on for Reactant that has you writing XML which is "live reloaded". It's not clear whether or not only the XML is eligible for live reloading or not.

Source: https://docs.reactant.tech/reactant-ui/introduction.html