Expansion level, reflecting the size of the lookalike audience

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v26/enums/lookalike_expansion_level.proto)

| Enums ||
|---|---|
| ## `BALANCED` | Expansion to a medium set of users that are similar to the seed lists. Includes all users of EXPANSION_LEVEL_NARROW, and more. |
| ## `BROAD` | Expansion to a large set of users that are similar to the seed lists. Includes all users of EXPANSION_LEVEL_BALANCED, and more. |
| ## `NARROW` | Expansion to a small set of users that are similar to the seed lists |
| ## `UNKNOWN` | Invalid expansion level. |
| ## `UNSPECIFIED` | Not specified. |