gEDA-dev: Question about Gerber output of PCB

[Stuart Brorson]

I have been looking at the drill files produced by PCB.  Here's a
sample from an old board of mine:

M48
INCH,TZ
T21C0.028
T22C0.040
T23C0.125
%
T21
X011450Y008700
X010950Y009200
X010450Y008700
X009950Y009200
[.... etc ....]

My question:   Umm, is it correct syntax to just say "INCH" on a line?
According to websites I have looked at, you should use an M72 code to
specify English units.  c.f.

http://www.pcbmilling.com/Examples%20of%20Gerber%20and%20Excellon%20Data%20Files.htm

At least according to what I have read, the chars "IN" should place
the drill tool into "Image Name" mode, meaning that the tool will
think that this layer has a name "CH".

Or is my head wedged?

Cheers,

Stuart