I think this reads a bit better for the replacement:

``` ruby
`d`, `doc`, or `documentation`
```

...but I hold that opinion very loosely.  Not a merge blocker.

A potentially more important concern: these values usually come from the command line (e.g. `rspec --format spec`) and in that context we don't want a call site printed as there won't be one.  Maybe we can just change `CallerFilter` to return nil when there's no line outside rspec in the backtrace.  Or would it be better to deprecate/convert them in `option_parser.rb` with `:call_site => nil` for the CLI option and then also here for an `RSpec.configure` option?