Data Management Capabilities > Managing Configurable Products > Windchill Options and Variants Capabilities > Assigning Expressions > Validating Expressions
  
Validating Expressions
When you create an expression, the system validates the expression to make sure:
The expression is syntactically correct
The choices used in the expression exist in the assigned option set
The expression contains a valid alias as defined in the Option Manager
If an error is found, the expression is not saved.
Site-specific Validation
Companies can create their own method for validating assigned expressions, which are used on Part, PartUsageLink, PartUsageOccurances, and ExpressionAlias objects. To do this, you must implement a method “validate” in the interface com.ptc.windchill.option.expression.ExpressionValidator, and then set a Windchill property com.ptc.windchill.option.expression.ExpressionValidator=ext.custom.CustomValidator.
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Ability to assign advanced expressions and validate with customized validation is an advanced capability subject to a separate license entitlement.