The QR encoder's message.
The image encoder's or decoder's message.
The SVG rasteriser's message.
Why the colour was rejected.
Which argument was rejected and why.
The GIF encoder's message.
No fields: ffmpeg was not found on PATH.
How ffmpeg failed, with what it wrote to stderr when it ran.
The symbol's module count and the limit it exceeded.
The frames requested and the fragments the message needs.
The file-system error's message and, when known, the path.
The uniform-resources error's message.
The structured payload each MurErrorCode carries.