Bash sort command numeric sort, fields and dictionary sort

Can you explain sort +0nr -2 +2d please? This example is from https://www.grymoire.com/Unix/Awk.html The comment says:

# numeric sort - biggest numbers first
# sort fields 0 and 1 first (sort starts with 0)
# followed by dictionary sort on fields 2 + 3

Please explain every argument used.

Thanks!

This is an obsolete (or at least obsolescent) "traditional" syntax for specifying field and column values, documented in info sort:

   On systems not conforming to POSIX 1003.1-2001, ‘sort’ supports a
traditional origin-zero syntax ‘+POS1 [-POS2]’ for specifying sort keys.
The traditional command ‘sort +A.X -B.Y’ is equivalent to ‘sort -k
A+1.X+1,B’ if Y is ‘0’ or absent, otherwise it is equivalent to ‘sort -k
A+1.X+1,B+1.Y’.

In the example you quote:

sort +0nr -2 +2d

there are two sets of specifiers: "+0 -2" and "-2". The first has A=0, B=2, Y absent and hence is equivalent to -k0+1,2 i.e. -k1,2 in in the modern 1-based indexing. The second has A=2 with both B and Y absent so becomes just -k3.

Letter options have their usual meanings i.e.

   -d, --dictionary-order
          consider only blanks and alphanumeric characters

   -n, --numeric-sort
          compare according to string numerical value

   -r, --reverse
          reverse the result of comparisons

so the result is reverse numeric sort on the first two fields, -k1,2nr followed by dictionary sort on the third (and following) fields -k3d.

The info page advises against using this form of syntax:

   Scripts intended for use on standard hosts should avoid traditional
syntax and should use ‘-k’ instead.  For example, avoid ‘sort +2’, since
it might be interpreted as either ‘sort ./+2’ or ‘sort -k 3’.  If your
script must also run on hosts that support only the traditional syntax,
it can use a test like ‘if sort -k 1 </dev/null >/dev/null 2>&1; then
...’ to decide which syntax to use.

it is the same as sort -k1,2nr -k3d.