Script Editor Question -- How to access pre-defined controls?

In the Script Editor:
I am trying to see whats in my txtSoldToCustID field on the screen but I can't access it as easily as I can the Custom text control which is just using its name e.g. txtOnHold.Name
I get an error message for the pre-defined text control if used by its name e.g. txtSoldToCustID.Value

Do I need to reference it somehow?

Please let me know if there is more info needed from the properties of the two controls in order to answer my question.

This is probably an easy one but I am a newbie to this world!
Thanks in advance!