The ability to omit the system identifier shall be an optional feature, and implies the availability of an external mapping mechanism. 10.2 Formal public identifier a. FPI syntax is in effect a data content notation. The presentation of the FPI syntax must be defined rigorously. Public Text Class a. The list of classes shall be a recommendation, not mandatory.
Further explanation is needed.
Public text display version a. The role of this component should be reconsidered in the light of the altreps data attribute and the entuse storage manager. 10.3 Comment Declaration a. The ability to have more or fewer than exactly one comment in a comment declaration shall be an optional feature. When exactly one comment is permitted, the com delimiters shall be concatenated with the adjacent declaration delimiters.