code: public function visit(Criterion $criterion, CriterionVisitor $subVisitor = null)
      {
          $queries = array();
          $values = (array)$criterion->value;
  
          foreach ($values as $value) {
              $preparedValue = $this->escapeQuote($this->toString($value), true);
  
              if ($this->isRegExp($preparedValue)) {
                  $queries[] = $criterion->target . ':' . $preparedValue;
              } else {
                  $queries[] = $criterion->target . ':"' . $preparedValue . '"';
              }
          }
  
          return '(' . implode(' OR ', $queries) . ')';
      }
docs: Map field value to a proper Solr representation.
  
  @param \eZ\Publish\API\Repository\Values\Content\Query\Criterion $criterion
  @param \EzSystems\EzPlatformSolrSearchEngine\Query\CriterionVisitor $subVisitor
  
  @return string