Custom filters documentation

[BrandonGillis]

When looking at the custom filters documentation there's multiple example of custom filters, but with different "alias".
There's this first example with o used as an hardcoded alias (REGEXP(o.%s, :%s)).

    protected function filterProperty(string $property, $value, QueryBuilder $queryBuilder, QueryNameGeneratorInterface $queryNameGenerator, string $resourceClass, Operation $operation = null, array $context = [])
    {
        // otherwise filter is applied to order and page as well
        if (
            !$this->isPropertyEnabled($property, $resourceClass) ||
            !$this->isPropertyMapped($property, $resourceClass)
        ) {
            return;
        }

        $parameterName = $queryNameGenerator->generateParameterName($property); // Generate a unique parameter name to avoid collisions with other filters
        $queryBuilder
            ->andWhere(sprintf('REGEXP(o.%s, :%s) = 1', $property, $parameterName))
            ->setParameter($parameterName, $value);
    }

Others example use the rootAliases :

//App/Filter/CustomAndFilter.php
protected function filterProperty(string $property, $value, QueryBuilder $queryBuilder, QueryNameGeneratorInterface $queryNameGenerator, string $resourceClass, Operation $operation = null, array $context = []) {  
  $rootAlias = $queryBuilder->getRootAliases()[0];  
  foreach (array_keys($this->getProperties()) as $prop) { //NOTE: we use array_keys because getProperties() returns a map of property => strategy
      if (!$this->isPropertyEnabled($prop, $resourceClass) || !$this->isPropertyMapped($prop, $resourceClass)) {  
          return;  
      }  
      $parameterName = $queryNameGenerator->generateParameterName($prop);  
      $queryBuilder  
          ->andWhere(sprintf('%s.%s LIKE :%s', $rootAlias, $prop, $parameterName))  
          ->setParameter($parameterName, "%" . $value . "%");  
  }  
}

Is there any reason that o was used as an alias in the first example ? What could it do if I use the same hardcoded alias (o) in my project ?