How to identify a field is read only from expression language(Page Composer)

Summary:

Hi, We are trying to make some of the DFF on the AR transaction line level as read only when the transaction is accounted. At header level we have posted to GL flag binding parameter. But at line level we do not have this. We raised an Oracle SR to provide the same field at the line level. But we have received an alternative workaround to check whether amount or quantity is read only(when transaction is accounted, these fields will become read only) and based on that we need to make DFF fields read only. Following is the SR for