Outdated: Only lowercase service and parameter names are allowed in service definitions

⚠️ Changed in Drupal 9.5.0! - see https://www.drupal.org/node/3320387

When defining services and service parameters, only lowercased names are allowed. Drupal will throw an \InvalidArgumentException if a developer uses uppercased names.

Before, this would be allowed:

$container->register('DefaultConfigTest.schema_storage');
$container->setParameter('persistIds', $persist_ids);

Drupal 8 & <= 9.4

Now, service and parameter names must be lowercased. As a best-practice, it is recommended, but not required, to use underscores "_" instead of CamelCase:

$container->register('default_config_test.schema_storage');
$container->setParameter('persist_ids', $persist_ids);

However defaultconfigtest would also work - as long as there are no uppercase characters.

Drupal 9.5 & 10

Now, only parameter names must be lowercased. As a best-practice, it is recommended, but not required, to use underscores "_" instead of CamelCase:

$container->setParameter('persist_ids', $persist_ids);

See https://www.drupal.org/node/3320387