The ``fish_clipboard_paste`` function copies text from the system clipboard.
If its stdout is not a terminal (see :doc:`isatty <isatty>`), it will output everything there, as-is, without any additional newlines. If it is, it will put the text in the commandline instead.
If it outputs to the commandline, it will automatically escape the output if the cursor is currently inside single-quotes so it is suitable for single-quotes (meaning it escapes ``'`` and ``\\``).