# Extensibility As almost every system evolves, one of the design goals is to make the system flexible enough to support new content types. The crawler can be extended by plugging in new modules * The PNG Downloader module is plugged-in to download PNG files. * Web Monitor module is added to monitor the web and prevent copyright and trademark infringements. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://huy312100.gitbook.io/software-development/system-design/fundamental/design-a-web-crawler/step-3-design-deep-dive/extensibility.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.