http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5. 
package org.bouncycastle.asn1;


Marker interface for CHOICE objects - if you implement this in a role your
own object any attempt to tag the object implicitly will convert the tag to
an explicit one as the encoding rules require.


If you use this interface your class should also implement the getInstance
pattern which takes a tag object and the tagging mode used. 

/**
 * Marker interface for CHOICE objects - if you implement this in a role your
 * own object any attempt to tag the object implicitly will convert the tag to
 * an explicit one as the encoding rules require.
 * <p>
 * If you use this interface your class should also implement the getInstance
 * pattern which takes a tag object and the tagging mode used. 
 */
public interface ASN1Choice
{
    // marker interface
}