POSIX.1-2024 is simultaneously IEEE Std 1003.1™-2024 and The Open Group Standard Base Specifications, Issue 8. POSIX.1-2024 defines a standard operating system interface and environment, including a command interpreter (or “shell”), and common utility programs to support applications portability at the source code level. POSIX.1-2024 is intended to be used by both application developers and system implementors and comprises four major components (each in an associated volume): --General terms, concepts, and interfaces common to all volumes of this standard, including utility conventions and C-language header definitions, are included in the Base Definitions volume. --Definitions for system service functions and subroutines, language-specific system services for the C programming language, function issues, including portability, error handling, and error recovery, are included in the System Interfaces volume. --Definitions for a standard source code-level interface to command interpretation services (a “shell”) and common utility programs for application programs are included in the Shell and Utilities volume. --Extended rationale that did not fit well into the rest of the document structure, which contains historical information concerning the contents of POSIX.1-2024 and why features were included or discarded by the standard developers, is included in the Rationale (Informative) volume.
The document itself is paywalled like all the POSIX specifications, so here are some highlights courtesy of some comments at HackerNews, especially from a-french-anon.
IMO the NUL-delimited options are by far the biggest win for shell scripting. $' ' will be the most commonly used addition, but "$(printf '...')" was always an option before. You don’t really have an alternative read -d ''.