The ASN.1 Compiler

I'm assuming asn1c doesn't support Extension Addition Groups as I get an error message with the following but perhaps someone could confirm this. Many thanks.

FooBar {1 2 3 4 5 6} DEFINITIONS ::= BEGIN
  ExtAddGrpEg ::= SEQUENCE {
    a INTEGER (250..253),
    b BOOLEAN,
    c BOOLEAN,
    ...,
    [[
      g NUMERICSTRING (SIZE (3..3)),
      h BOOLEAN OPTIONAL
    ]],
    ...,
    i BMPSTRING OPTIONAL,
    j PrintableString OPTIONAL
  }
END