edge of word atom in PG regex engine?

Hello,

    I am trying to match the following:

    select '4:5:67'::text ~ '4'::text as match;
     match
    -------
     t
    (1 row)

but I would like to avoid '44:5:67' matching '4' so I tried including
"word edge" regexp atoms (\b in perl, \<\> in grep and vi, etc..) but
they don't seem to be supported in Postgres:

    select '4:5:67'::text ~ '\<4\>'::text as match;
     match
    -------
     f
    (1 row)

    select '4:5:67'::text ~ '\b4\b'::text as match;
     match
    -------
     f
    (1 row)

Is there an equivalent under Postgres?

Thanks in advance,

--
Louis-David Mitterrand - ldm@apartia.org - http://www.apartia.org

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