Regardless of which mode you are (visual or source), the subject is treated as wikitext. Also in both modes we style the input with the same font as the final rendering, something we only usually do in visual modes (in source mode we usually use monospace to indicate wikitext).
In source mode there is at least a preview to help you catch any errors.
| Discussion tools visual mode | After publishing |
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| Discussion tools source mode | After publishing |
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Flow does not give us an example of what to do here, as it disables all formatting in the topic title, which we can't do without it being a regression from the old new topic tool.