Issue #3417363 by narendraR, Wim Leers, catch, phenaproxima, alexpott: Add...

field_ui.settings:

  type: config_object

  label: 'Field UI settings'

  constraints:

    FullyValidatable: ~

  mapping:

    field_prefix:

      type: string

      label: 'The prefix for new fields created via Field UI'

      constraints:

        Regex:

          # @see \Drupal\field\Entity\FieldStorageConfig::__construct()

          pattern: '/^[_a-z]+[_a-z0-9]*$/'

          message: "The %value prefix is not valid."

        Length:

          # The maximum length of the field name is 32 characters. This maximum

          # length also encompasses the length of the field_prefix, which is

          # capped at 30 characters here. By setting the field_ui.settings:field_prefix config

          # to its maximum length, only two characters will remain available

          # for the actual field name based on the above specified pattern.

          # @see \Drupal\field\Entity\FieldStorageConfig::NAME_MAX_LENGTH

          # @see \Drupal\field\Entity\FieldStorageConfig::preSaveNew()

          max: 30