Enum describing matching info source for Search Lift.

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

| Enums ||
|---|---|
| ## `CONTROL` | Random keywords used to evaluate measure, for which we expect no lift. |
| ## `SINGLE_KEYWORD` | Specifies a single keyword from a set of keywords. |
| ## `SURVEY_COMPETITOR_OPTION` | Matching info is based on the survey lift competitor option. |
| ## `SURVEY_PREFERRED_OPTION` | Matching info is based on the survey lift preferred option. |
| ## `UNKNOWN` | Used for return value only. Represents value unknown in this version. |
| ## `UNSPECIFIED` | Not specified. |
| ## `USER` | Matching info is based on user input. |