Help with reg_exp

[I mistakenly used the wrong Subject line initially with this post]

In going through the arcana of string functions, I have come across the
following series of selects that contain, for me, a mysterious "$re$".

-- return all matches from regexp
SELECT regexp_matches('
foobarbequebaz', $re$(bar)(beque)$re$);

-- test case insensitive
SELECT regexp_matches('foObARbEqUEbAz', $re$(bar)(beque)$re$, 'i');

-- global option - more than one match
SELECT regexp_matches('foobarbequebazilbarfbonk', $re$(b[^b]+)(b[^b]+)$re$,
'g');

When I run this I get:

regexp_matches
--------------------------
<Unknown(2,003)>

I have not been able to find out what it all means. Forgive me for my
blindness.

John

P.S. The author of the statements is "alexk" at Command Prompt. They are
test statements against Postgres' string functions.