Create a PlainTextContentBlock.
The id is generated automatically if not provided, using a UUID4 format
prefixed with 'lc_' to indicate it is a LangChain-generated ID.
Base64-encoded plaintext data.
ID of the plaintext file from a file storage system.
Title of the text data.
Context or description of the text content.
Content block identifier.
Generated automatically if not provided.
Index of block in aggregate response.
Used during streaming.