[Retrievers](https://js.langchain.com/docs/concepts/retrievers/): LLM should read this page when (needing to understand how retrievers work in LangChain, implementing RAG systems, or comparing different retrieval approaches) (Explains retrievers in LangChain which provide a standard interface for retrieving documents using natural language queries. Covers the basic retriever interface, common types including search APIs, relational/graph databases, lexical search, and vector stores. Discusses advanced patterns like ensemble retrievers and source document retention strategies including ParentDocument and MultiVector retrievers.)

