code: public boolean hasMixinType( AstNode node,
                                   String mixinType ) {
          CheckArg.isNotNull(node, "node");
          CheckArg.isNotNull(mixinType, "mixinType");
          return node.getMixins().contains(mixinType);
      }
docs: Utility method to determine if an {@link AstNode} contains a specific mixin type.
  
  @param node the AstNode
  @param mixinType the target mixin type {@link String}; may not be null;
  @return true if the mixinType exists for this node