umber.
- `s`: formatted as a string, precision indicates padding and maximum length.
- `t`: emit the type of the given value.
- `v`: format with (describe x)
- `V`: format with (string x)
- `j`: format to jdn (Janet data notation).

The following conversion specifiers are used for "pretty-printing", where the upper-case variants generate colored output. These specifiers can take a precision argument to specify the maximum nesting depth to print.
- `p`, `P`: pretty format, truncating if necessary
- `m`, `M`: