xml - What does i:nil="true" mean?

Question

I have an xml and it has nodes with i:nil="true" in it. What does that mean?

For example:

<FirstName i:nil="true" />

Does that mean something different than:

<FirstName />

If so, what is the difference?

Answer 1

This means FirstName is null

<FirstName i:nil="true" />

This means FirstName = ""

<FirstName />

Assumption made on FirstName is of string type.