start_sequence

static VALUE start_sequence(
        VALUE self,
        VALUE anchor,
        VALUE tag,
        VALUE implicit,
        VALUE style
        ) {
    yaml_emitter_t * emitter;
    yaml_event_t event;

    rb_encoding * encoding = rb_utf8_encoding();

    if(!NIL_P(anchor)) {
        Check_Type(anchor, T_STRING);
        anchor = rb_str_export_to_enc(anchor, encoding);
    }

    if(!NIL_P(tag)) {
        Check_Type(tag, T_STRING);
        tag = rb_str_export_to_enc(tag, encoding);
    }

    TypedData_Get_Struct(self, yaml_emitter_t, &psych_emitter_type, emitter);

    yaml_sequence_start_event_initialize(
            &event,
            (yaml_char_t *)(NIL_P(anchor) ? NULL : StringValueCStr(anchor)),
            (yaml_char_t *)(NIL_P(tag) ? NULL : StringValueCStr(tag)),
            implicit ? 1 : 0,
            (yaml_sequence_style_t)NUM2INT(style)
            );

    emit(emitter, &event);

    return self;
}