src/Routing/Route.php
public function getResourceId(): ?string
    {
        if (is_null($this->resourceId)) {
            return $this->parameter(ResourceRegistrar::PARAM_RESOURCE_ID);
        }

        return $this->resourceId ?: null;
    }
public function getResourceId(): ?string
    {
        if (is_null($this->resourceId)) {
            return $this->parameter(ResourceRegistrar::PARAM_RESOURCE_ID);
        }

        return $this->resourceId ?: null;
    }
What is the resource id of the route?

@return string|null