$ openssl asn1parse -i < [BASIC CONSTRAINTS]
    0:d=0  hl=2 l=   6 cons: SEQUENCE          
    2:d=1  hl=2 l=   1 prim:  BOOLEAN           :255
    5:d=1  hl=2 l=   1 prim:  INTEGER           :09
-----BEGIN BASIC CONSTRAINTS-----
MAYBAf8CAQk=
-----END BASIC CONSTRAINTS-----