zsh: Abbreviation expansion, what does |& mean?

Question

The grml zsh configuration contains a zsh abbreviation for a command I have never seen before:

abk=(
#   key   # value                  (#d additional doc string)
#A# start
    # <snipped>
    'G'    '|& grep --color=auto '

I am wondering why the abbreviation G expands to |& and not |. So the question is:

What is the difference between |& and |?

Answer 1

|& is short form for 2>&1 | – it redirects both stdout and stderr over the pipe.