When creating calculations or scripts to enhance your form, you should be aware of the form design object and variable names on your form. In general, your form should avoid using the names of XML Form Object Model properties, methods, and objects for form design objects and variables. Using XML Form Object Model property, method, or object names can result in calculations and scripts not executing properly.
For example, if you create a new text field named x within a subform object named Subform1, you access the text field object using the following syntax:
Subform1.x.[expression]
However, subform objects already have an XML Form Object Model property named x that represents the horizontal position of the subform on the form design.
To avoid naming conflicts, you need to choose field naming conventions that differ from the XML Form Object Model naming conventions. For example, you can use any of the following field names for the text field in the example above:
See also 

Naming conventions for form design objects and variables