@piojo like this better?
```
relay.backends: [% relay.backends.join(" \\\n    ") %]
[%- relay.delete('backends') -%]
[%- FOREACH base IN ['hash', 'relay', 'overflow'] -%]
[%-     FOREACH pair IN ${base}.pairs %]
[%          base %].[% pair.key %]: [% pair.value %]
[%-     END -%]
[%- END %]
```