In these lines, you declare explicit error messages for the controls written with specific code.
The controls coded on the Data Element calls in Data Structures are the only ones that trigger the automatic generation of error messages. For all the errors detected by other controls, automatic or otherwise, error messages must be defined explicitly here.
Moreover, if this line is not correct, this column also displays an error or warning symbol, depending on the error gravity. A hover help indicates the source of the error.