protected function getResource($resource)
    {
        // If the resource was found before, we can speed things up
        // by caching its absolute, resolved path:
        if (isset($this->resourceCache[$resource])) {
            return $this->resourceCache[$resource];
        }

        // Search through available search paths, until we find the
        // resource we're after:
        foreach ($this->searchPaths as $path) {
            $fullPath = $path . "/$resource";

            if (is_file($fullPath)) {
                // Cache the result:
                $this->resourceCache[$resource] = $fullPath;
                return $fullPath;
            }
        }

        // If we got this far, nothing was found.
        throw new RuntimeException(
            "Could not find resource '$resource' in any resource paths."
            . "(searched: " . join(", ", $this->searchPaths). ")"
        );
    }