system/Router/RouteCollection.php
private function checkSubdomains($subdomains): bool
	{
		// CLI calls can't be on subdomain.
		if (! isset($_SERVER['HTTP_HOST']))
		{
			return false;
		}

		if (is_null($this->currentSubdomain))
		{
			$this->currentSubdomain = $this->determineCurrentSubdomain();
		}

		if (! is_array($subdomains))
		{
			$subdomains = [$subdomains];
		}

		// Routes can be limited to any sub-domain. In that case, though,
		// it does require a sub-domain to be present.
		if (! empty($this->currentSubdomain) && in_array('*', $subdomains))
		{
			return true;
		}

		foreach ($subdomains as $subdomain)
		{
			if ($subdomain === $this->currentSubdomain)
			{
				return true;
			}
		}

		return false;
	}
private function checkSubdomains($subdomains): bool
	{
		// CLI calls can't be on subdomain.
		if (! isset($_SERVER['HTTP_HOST']))
		{
			return false;
		}

		if (is_null($this->currentSubdomain))
		{
			$this->currentSubdomain = $this->determineCurrentSubdomain();
		}

		if (! is_array($subdomains))
		{
			$subdomains = [$subdomains];
		}

		// Routes can be limited to any sub-domain. In that case, though,
		// it does require a sub-domain to be present.
		if (! empty($this->currentSubdomain) && in_array('*', $subdomains))
		{
			return true;
		}

		foreach ($subdomains as $subdomain)
		{
			if ($subdomain === $this->currentSubdomain)
			{
				return true;
			}
		}

		return false;
	}
Compares the subdomain(s) passed in against the current subdomain
on this page request.

@param mixed $subdomains

@return boolean