system/Config/BaseConfig.php
protected function registerProperties()
	{
		if (! static::$moduleConfig->shouldDiscover('registrars'))
		{
			return;
		}

		if (! static::$didDiscovery)
		{
			$locator         = \Config\Services::locator();
			$registrarsFiles = $locator->search('Config/Registrar.php');

			foreach ($registrarsFiles as $file)
			{
				$className = $locator->getClassname($file);
				static::$registrars[] = new $className();
			}

			static::$didDiscovery = true;
		}

		$shortName = (new \ReflectionClass($this))->getShortName();

		// Check the registrar class for a method named after this class' shortName
		foreach (static::$registrars as $callable)
		{
			// ignore non-applicable registrars
			if (! method_exists($callable, $shortName))
			{
				continue;
			}

			$properties = $callable::$shortName();

			if (! is_array($properties))
			{
				throw new \RuntimeException('Registrars must return an array of properties and their values.');
			}

			foreach ($properties as $property => $value)
			{
				if (isset($this->$property) && is_array($this->$property) && is_array($value))
				{
					$this->$property = array_merge($this->$property, $value);
				}
				else
				{
					$this->$property = $value;
				}
			}
		}
	}
protected function registerProperties()
	{
		if (! static::$moduleConfig->shouldDiscover('registrars'))
		{
			return;
		}

		if (! static::$didDiscovery)
		{
			$locator         = \Config\Services::locator();
			$registrarsFiles = $locator->search('Config/Registrar.php');

			foreach ($registrarsFiles as $file)
			{
				$className = $locator->getClassname($file);
				static::$registrars[] = new $className();
			}

			static::$didDiscovery = true;
		}

		$shortName = (new \ReflectionClass($this))->getShortName();

		// Check the registrar class for a method named after this class' shortName
		foreach (static::$registrars as $callable)
		{
			// ignore non-applicable registrars
			if (! method_exists($callable, $shortName))
			{
				continue;
			}

			$properties = $callable::$shortName();

			if (! is_array($properties))
			{
				throw new \RuntimeException('Registrars must return an array of properties and their values.');
			}

			foreach ($properties as $property => $value)
			{
				if (isset($this->$property) && is_array($this->$property) && is_array($value))
				{
					$this->$property = array_merge($this->$property, $value);
				}
				else
				{
					$this->$property = $value;
				}
			}
		}
	}
Provides external libraries a simple way to register one or more
options into a config file.

@throws \ReflectionException