[Migration]: Vue 3 doesn't replace the element it mounts to

[LinusBorg]

I'm Vue 2, the element we mount to is replaced. In Vue 3, because we now have Fragements, we mount the app as a child of the mount element.

We don't really document this clearly, at least I couldn't find anything by skimming migration guide and api docs.

[skirtles-code]

The migration guide sort of mentions it indirectly here:

https://v3.vuejs.org/guide/migration/introduction.html#other-minor-changes

In Vue 2.x, application root container's outerHTML is replaced with root component template (or eventually compiled to a template, if root component has no template/render option). Vue 3.x now uses application container's innerHTML instead - this means the container itself is no longer considered part of the template.

Perhaps that should get a page to itself and be less focused on the template aspect of the change?

It should probably be mentioned more explicitly in the API Reference for mount:

https://v3.vuejs.org/api/application-api.html#mount

The API reference for template also needs updating. It claims the element is 'replaced', which is no longer true. Given a template option can be used on any component, not just the root component, it probably shouldn't focus quite so heavily on that aspect anyway:

https://v3.vuejs.org/api/options-dom.html#template

[LinusBorg]

This section in the migration guide could also be a good place to mention it:

https://v3.vuejs.org/guide/migration/global-api.html#mounting-app-instance

[LinusBorg]

Another point: in the lifecycle diagram, it states:

Create app.$el and replace el with it

Should probably be

Create app.$el and append it to el