Raw Block

A block of pre-formatted content in a declared media type. Borrowed from Pandoc's AST. Use for content that is already in a specific format (e.g., a markdown-formatted section body, a JSON snippet, an HTML fragment) and should be either parsed natively by backends that understand the format, or passed through verbatim by those that don't. This is how the transformation system expresses "this string is markdown, not plain text". A Markdown backend emits the `rawContent` verbatim because the content is already markdown; an HTML backend dispatches on `mediaType` and runs text/markdown content through its own markdown renderer before emitting HTML; a JSON backend serializes the RawBlock as a structured object with both channels. Pandoc's `RawBlock(format, content)` is the direct analogue.