regex help wanted

Hi,

I am in the process of converting some TEXT data which I try
to identify by regular expression.

What I don't understand is: Why does the following return a
substring ?

    select substring ('junk $<allergy::test::99>$ junk' from '\$<[^<]+?::[^:]+?>\$');

I would have thought the '::[^:]+?>' part should have meant

    after two ":"s
    match at least one character
    except any further ":"s
    until the next ">"

I don't find the flaw in my thinking. Can anyone help ?

(Sure, it is not PostgreSQL-specific yet I need to run this
in PostgreSQL on data migration.)

Karsten
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