@Override
    public void setAlphanumericOnlyRefs(boolean alphanumericOnlyRefs) {
        // CloudFormation Resource Schemas MUST use alphanumeric only references.
        // Throw if customers tried to set it to false.
        //
        // https://github.com/aws-cloudformation/cloudformation-cli/blob/master/src/rpdk/core/data/schema/provider.definition.schema.v1.json#L303
        if (!alphanumericOnlyRefs) {
            throw new CfnException("CloudFormation Resource Schemas MUST use alphanumeric only "
                    + "references. `alphanumericOnlyRefs` value of `false` was provided.");
        }
    }
The JSON pointer to where CloudFormation schema shared resource properties should be written.
smithy-aws-cloudformation/src/main/java/software/amazon/smithy/aws/cloudformation/schema/CfnConfig.java