Meaning of exclamation point in front of variable?

I have encountered some PBPro code that has an exclamation point in front of some of the declared variables. I find no definition of that syntax in the PBPro manual. For example: IF !Plugged THEN

Can anyone tell me what the exclamation point means?? I see it used on the variable in the code contained in an INCLUDE file and not used in the main code for the same variable name.

IF NOT Plugged THEN

It's listed under "Logical Operators".
Page 43 in the latest manual.
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Originally Posted by Darrel Taylor

IF NOT Plugged THEN

It's listed under "Logical Operators".
Page 43 in the latest manual.
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Thanks, Darrel. I feel stupid to not have found that. I looked right over it. I now understand the logic of your code better.