core[patch]: Add doc-string to document compressor (#23085)

libs/core/langchain_core/documents/compressor.py

@@ -10,7 +10,20 @@ from langchain_core.runnables import run_in_executor
 
 
 class BaseDocumentCompressor(BaseModel, ABC):
-    """Base class for document compressors."""
+    """Base class for document compressors.
+
+    This abstraction is primarily used for
+    post-processing of retrieved documents.
+
+    Documents matching a given query are first retrieved.
+    Then the list of documents can be further processed.
+
+    For example, one could re-rank the retrieved documents
+    using an LLM.
+
+    **Note** users should favor using a RunnableLambda
+    instead of sub-classing from this interface.
+    """
 
     @abstractmethod
     def compress_documents(