What's the "In" used for?

["ephjyin" <ephjyin@xxxxxxxxx>]

Dear David,
I tried the FEMM, it's a great thing! But I have a thing unclear. 
There are three "In"'s in the "Properties for selected Block" 
dialogue box and in the "Specify nodal property" dialogue box. I know 
the first "In" in the "Properties for selected block" is for the 
circuit selecting, but I do not know what the other two are used for. 
I have tried put different values in their blanks, and did not find 
any effects on the results. Hope you can make a readme file for these 
entries. Thank you.