Owl is a declarative component system: we declare the structure of the component tree, and Owl will translate that to a list of imperative operations. This translation is done by a virtual dom. This is the low level layer of Owl, most developer will not need to call directly the virtual dom functions.
The main idea behind a virtual dom is to keep a in-memory representation of the DOM (called a virtual node), and whenever some change is needed, to regenerate a new representation, compute the difference between the old and the new, then apply the changes.
vdom exports two functions:
h: create a new virtual nodepatch: compare two virtual nodes, and apply the difference.
Note: Owl's virtual dom is a fork of snabbdom.