Note that, in public identifiers, letter case and the presence of spaces and record ends are significant. More precisely, a record end is treated as a space, and then a run of consecutive spaces is treated as a single space; therefore, while a record end and extra spaces can be inserted wherever a single space is shown, neither a record end nor a space may be inserted where no space is shown, including immediately before or after the double slashes.
3.4 DOCUMENT INSTANCE. The document instance shall conform to ISO 8879, the SGML declaration in 3.9 (or an acceptable modification thereof), and to the contractually specified DTD.
3.5 FORMATTING OUTPUT SPECIFICATION INSTANCE (FOSI). A FOSI shall
conform to the Output Specification (OS) in appendix B and to ISO 8879. A FOSI shall specify a layout object for each unique page, frame, or screen. Layout object characteristics shall be as specified in the contract or other form of agreement. Presentation characteristics of every displayable element declared in the source DTD shall be specified in the FOSI. Values for presentation characteristics shall be as specified in the contract (see 6.2). The inheritance of presentation characteristics for elements within a content model of the source DTD shall be as specified in the OS.