Wrong cell-option marker for a diagram cell
%%, so its cell options are %%| — #| is not a mermaid comment.
Q-2-48 — Wrong cell-option marker for a diagram cell
#|is not a mermaid comment, so these lines are read as diagram source.
What this means
Cell options are written in the cell language’s own comment syntax.
Python and R comment with #, so their options are #|. Mermaid
comments with %%, so its options are %%|:
```mermaid
%%| fig-cap: The review cycle.
flowchart LR
Draft --> Review
```A block that starts with #| instead has no cell options at all —
Quarto sees ordinary diagram content:
```mermaid
#| fig-cap: The review cycle.
flowchart LR
Draft --> Review
```Because # means nothing to Mermaid either, those lines are handed to
the diagram renderer as part of the diagram, and Mermaid fails to parse
them. The result is a broken drawing with no caption — which is why
Quarto reports it here rather than letting the failure surface in the
browser console.
Why this happens
Almost always familiarity with #| from Python and R cells. The marker
is not universal: it tracks the language, so --| serves Lua and SQL,
//| serves JavaScript and Rust, and %%| serves Mermaid.
Earlier Quarto 2 versions accepted #| inside a ```mermaid
fence. That was a bug, and accepting it taught the wrong rule; Quarto 2
now matches Quarto 1 and takes %%| only.
How to fix
Change the marker:
```mermaid
%%| fig-cap: The review cycle.
flowchart LR
Draft --> Review
```Nothing else needs to change — the option names and values are the same.