Consider an option to specify the total length of Void elements (header and payload)

[StokesMIDE]

The Void element is intended largely as padding. As such, it would be useful to be able to specify a total size for the element, not just the size of its payload. For example, a Void with a specified length of 100 would write 0xEB+0xE2+(0xFF * 98). The only trick is calculating the length of the length, but that could be made easier by writing longer lengths than required (e.g. 0x10000062 instead of 0xE2); since this is padding, wasting space isn't really an issue.