What does "XID" mean?

I can't imagine what that stands for.

I downloaded a titleblock to look at and one of his layers for the lines that made up the bounderies of the titleblock, was placed on the "XID" layer. It was interesting to see that the lines had the properties of Polyline, although to my eyes it looked like a line segment.

So, would anyone know what XID stands for in this case?

Thanks.

It may be a hold over from the early short format AIA layering names. I actually have that layer in my titleblocks and I don't remember where it came from or why I continue to use it other than it hasn't caused me any problems so I just leave it alone.

Cue wild guessing. Why do CAD people give wildly different names to the same thing? If only there were some kind of guideline...

eXternal Inline Divider?

Only thing I can find is eXchange IDentifier...whatever the heck that is.

What ever happened to layers that were called "walls", "doors", "windows", "steel"...? No..can't do it that way. Even though you can name them anything you want, gotta keep the cryptographers in a job coming up with layer names that are impossible to decipher.

Layer A

Layer A1

Layer A2

Layer A3...

What's the next layer?

Nope.

Layer RED.