# H.4. Extensions PostgreSQL is designed to be easily extensible. For this reason, extensions loaded into the database can function just like features that are built in. The `contrib/` directory shipped with the source code contains several extensions, which are described in [Appendix F](https://www.postgresql.org/docs/10/static/contrib.html). Other extensions are developed independently, like [PostGIS](http://postgis.net/). Even PostgreSQL replication solutions can be developed externally. For example, [Slony-I](http://www.slony.info/) is a popular master/standby replication solution that is developed independently from the core project. --- # 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://docs.postgresql.tw/14/appendixes/h.-wai-bu-zhuan-an/h.4.-extensions.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.