Drupal 8.3 introduced some changes, which broke a custom module; fixing the changes causes the module to break in previous Drupal versions. One way to handle this would be to require Drupal core to above version 8.3+ for this module. However, the following changes to YAML file does not work.
core: '8.3' core: '8.3.x'
Drupal shows the following incompatibility message.
This version is not compatible with Drupal 8.x and should be replaced.
The official documentation does not provide useful information for core keyword.
So how should Drupal core version requirement specified in the .info file? If not, is there any other way to specify such requirement?