A function which will be called when the UrlFragmentCore wants to set the hash in the browser.
To be called when the hash fragment in the browser URL changes. (This is automatically set up in UrlFragment)
Setting a value in the hash fragment does not emit a corresponding value in the Observable from the
{@link UrlFragment#watch} methods. This is deliberate, to prevent accidental feedback loops, and to avoid that
the hash fragment is used as a component-to-component communications channel.
It is best to think of the URL fragment as a storage which a service/component can use to store and re-establish
its own state, not as a messaging system to other components.
As a (very strong) rule of thumb, a component should not set anything that it doesn't itself watch.
Returns an observable which will emit when the given key changes in the URL hash fragment.
This is the internal core of the hash fragment/deeplink functionality. You probably want the browser-enabled UrlFragment instance exported from
url-fragment.