``string join`` joins its STRING arguments into a single string separated by SEP, which can be an empty string. Exit status: 0 if at least one join was performed, or 1 otherwise.
``string join0`` joins its STRING arguments into a single string separated by the zero byte (NUL), and adds a trailing NUL. This is most useful in conjunction with tools that accept NUL-delimited input, such as ``sort -z``. Exit status: 0 if at least one join was performed, or 1 otherwise.
Because Unix uses NUL as the string terminator, passing the output of ``string join0`` as an *argument* to a command (via a :ref:`command substitution <expand-command-substitution>`) won't actually work. Fish will pass the correct bytes along, but the command won't be able to tell where the argument ends. This is a limitation of Unix' argument passing.
