When to use it
Most of the time you do not need this. Change the data and the elements bound to it follow, which is the
whole point of the framework.
It earns its place when the connection between data and element is not something Bindary can see. An element
whose content is computed rather than bound, a value derived from several keys or a case where you want one
element refreshed and deliberately not its neighbours. The id gives you a handle on exactly one element.
The id must be unique on the page. Two elements sharing one update-id is not a way to update
both.