[LangChain Expression Language (LCEL)](https://js.langchain.com/docs/concepts/lcel/): LLM should read this page when needing to understand LangChain Expression Language, looking for ways to optimize chain execution, or deciding between LCEL and LangGraph. (LCEL is a declarative approach for building chains from Runnables, offering benefits including optimized parallel execution, simplified streaming, LangSmith tracing, a standard API, and LangServe deployment. Key composition primitives include RunnableSequence for sequential operations and RunnableParallel for concurrent execution, with shorthand syntax like the pipe method for improved readability.)

