google 'vba format' to find out more - but depending on the datatype there are up 4 format conditions separated with a semi colon.
positive;negative;zero;null
numbers have 4 conditions, dates have 3 (no negative), text has 2 (no negative or zero)
One I have used on form controls would be for example
0.00;[red](0.00);"-","Please enter a number"
so depending on the control value they would appear as
so a positive number -> 12.22
a negative number -> (12.22)
a zero -> -
a null -> Please enter a number
Because these are format properties they do not affect the underlying data and you can appear to have text in a number control