WP_Date_Query::get_compare( array $query )

Source

File: wp-includes/class-wp-date-query.php

public function get_compare( $query ) {
		if ( ! empty( $query['compare'] )
			&& in_array( $query['compare'], array( '=', '!=', '>', '>=', '<', '<=', 'IN', 'NOT IN', 'BETWEEN', 'NOT BETWEEN' ), true )
		) {
			return strtoupper( $query['compare'] );
		}

		return $this->compare;
	}