Use If Get(ActiveModiferKeys)=16 with onObjectEnter script trigger. As long as you are pressing the command key when you enter the field it will be detected.
Thanks S Chamblee. That's what I've been trying, but with no luck. As a test, I created a simple script that is:
Show Custom Dialog [ get (ActiveModifierKeys) ]
Exit Script 
and trigger it from onObjectEnter. No matter what keys I press (and hold) the dialog always shows "0". UPDATE: Actually, just tried it on another field and triggered the script from a button to see if that difference would solve anything. Same (non) results. My keyboard is working, but Filemaker is not seeing these keys. Bug? FM setting? ???
I have tested and it works. Try this script
show custom dialog box["Command"]
If the Command key is press when you click into the filed the dialog box will display, if the command key is not press then the box will not show.
Here is a sample app https://www.sugarsync.com/pf/D9559058_78149901_187895
It will only detect the command button if it is pressed and held down when you enter the field. The script trigger will not trip if you press the command button while you are already in the field.
Thank you, S Chamblee. I downloaded your file, and…it did not work! I tried restarting FM, and still no luck. Shutdown and restarted the computer, and everything worked again. So, there was something going on with the Mac that was preventing the modifier keys from be detected by FM. I have no idea what that could be, but I thank you for your file. When that didn't work either, it showed there was something bigger going on.