The index of customer attributes.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v25/enums/listing_group_filter_custom_attribute_index.proto)

| Enums ||
|---|---|
| ## `INDEX0` | First listing group filter custom attribute. |
| ## `INDEX1` | Second listing group filter custom attribute. |
| ## `INDEX2` | Third listing group filter custom attribute. |
| ## `INDEX3` | Fourth listing group filter custom attribute. |
| ## `INDEX4` | Fifth listing group filter custom attribute. |
| ## `UNKNOWN` | Used for return value only. Represents value unknown in this version. |
| ## `UNSPECIFIED` | Not specified. |