Dependecies prefix coding standard Running phpcs --standard=DrupalPractice in several modules *.info.yml file I get a warning message: 

All dependencies must be prefixed with the project name


I've seen some modules that use the module name as prefix

dependencies:
  - modulename:modulename
  - modulename:submodulename


Others when it belongs to Drupal core:

dependencies:
  - drupal:modulename_already_in_core


Others when it belongs to always Drupal (doesn't taking into account if the module is in the core or not):

dependencies:
  - drupal:modulename


Which is the right syntax? Should I use "drupal" always? Just when the module is in Drupal (core)? What is the aim of this requirement?

Thanks!

More info: https://www.drupal.org/project/coder/issues/2854781
As described in Let Drupal 8 know about your module with an .info.yml file, the correct format is:


project-name:module-name for third-party modules
drupal:module-name for a core module



  Dependencies should be namespaced in the format: {project}:{module} where {project} is the project name as it appears in the Drupal.org URL (e.g. drupal.org/project/views) and {module} is the module's machine name.


Since the project page for Drupal core is https://www.drupal.org/project/drupal, the case for Drupal core modules is the same as for third-party modules.