If a source file is paired with a `.experimental` file (for example,
`foo.xml` has a silbing `foo.experimental` file), then it will be
precompiled using `--emit xmlo-experimental` instead of `--emit
xmlo`. Further, the contents of the experimental file may contain
`#`-prefixed comments describing why it exists, as well as additional
options to pass to `tamec`.
For example, if this is an experimental file:
```
--foo
--bar=baz
```
Then the tamec invocation will contain:
tamec [...] --emit xmlo-experimental --foo --bar=baz -o foo.xmli
This allows for package-level conditional compilation with new features so
that I am able to focus on packages that will provide the most meaningful
benefits to our team, whether they be performance or features.
DEV-13162