There are up to three parts to the format string, separated by semi-colons. Sometimes, one does anyhow. A sign which appears for positive numbers. An exponent which will be shown without a sign if positive. As seen near the end of the one-liners, the literals can be pretty much anything you want.
Some possibilities make more sense than others.
If you do this, a list of results is returned. For the most part, you won't use this, and any error or uncertainty reported by the toolbox is considered an error. Starting from fFormatOK at the top of the list with a value of 0, these are increasing numeric values. As usual, you get a table with all parameters of the reply event. And as usual, it's up to you to start with an empty table, and to check for a non-zero 'errn' parameter to indicate an error.