Identifies the expression that is applied by the transform. The value parameter can be one of the following types:

• test predicates that evaluate to Boolean values (value: myAge == '30' yields a true or false value), or
• computational expressions ( value: abs(pow(myCol,3)) ).

The expected type of value expression is determined by the transform type. Each type of expression can contain combinations of the following:

• literal values:  value: 'Hello, world'
• column references:  value: amountOwed * 10

• functions:   value: left(myString, 4)

• combinations:  value: abs(pow(myCol,3))

The types of any generated values are re-inferred by the platform.