Documentation doesn't explain record states

I can see that records have these four properties:
- isPending
- isRejected
- isRequested
- isResolved

I gather that when `isResolved = true` the `record.content` property is fulfilled and I can render my template. I'm guessing that `isRejected` is true if the load failed. What is the difference between `isPending` and `isRequested`?

Probably all four should be explained in the documentation with some sort of sample template logic. Example:

``` handlebars
{{#if record.isResolved}}
{{#with record.content as |model|}}

{{/with}}
{{else if record.isRejected}}

{{else}}

{{/if}}
```