The FORMAT record describes a number format in the workbook.
All the FORMAT records should appear together in a BIFF file. The order of FORMAT records in an existing BIFF file should not be changed. You can write custom number formats in a file, but they should be added at the end of the existing FORMAT records.
Record Data
Offset
Name
Size
Contents
4
ifmt
2
Format index code (for internal use only)
6
cch
1
Length of the format string
7
rgch
var
Number format string
Microsoft Excel uses the ifmt field to identify built-in formats when it reads a file that was created by a different localized version. For more information about built-in formats, see "XF" on page 426.