Meaning of S-shaped bag delimiters

It is sometimes assumed that the S-shaped bag delimiters (U+27C5 and
U+27C6) are for multisets (because multisets are also called “bags”).
However, looking at the attestation shown in N2680, they appear to be
used around a well-formed formula rather than for a multiset. This
suggests that “bag” simply describes their shape, though the
description “The second pair of proposed characters is a set of
s-shaped delimiters used as bag delimiters” in the proposal does make
it sound as though they were multiset delimiters.

https://www.unicode.org/L2/L2003/03410-n2680-add-math-chars.pdf

Given that the referenced document is no longer available, does anyone
know what these characters mean?