Raw diagram source. For indented fences, body lines retain the source
indentation prefix. The sentinel '__UNCLOSED_FENCE__' marks a fence with
no closing marker.
1-indexed column of the opening fence.
1-indexed line of the opening fence (or line 1 for whole-file .mmd).
Source file path the block came from.
Detected diagram type (e.g. 'flowchart', 'sequenceDiagram', 'unknown').
A single Mermaid diagram extracted from a source document, with the location of its opening fence and the raw diagram body.