Basically, CalDOM's reactivity system does not care how the Element is created as long as it's a Native DOM Element/Node.
It could be _("+div") or document.createElement("DIV") or even jQuery("<div></div>")
See example: https://caldom.org/#reactive-native-node
Also, a CalDOM instance is just a wrapper around Native DOM Element(s).
_("div").elem === document.querySelectorAll("div")[0]
This interoperability allows for powerful integrations & to update the DOM directly by avoiding expensive virtual-DOM diffing.
In React's world, everything is micro-managed(there're pros & cons), accessing DOM directly can be chaotic & usually not recommended.