          :validators="{ required: true, minlength: 4 }"
                @valid="handleValid" 
                @invalid="handleInvalid" 
                @touched="handleTouched" 
                @dirty="handleDirty" 
                @modified="handleModified">
        <input type="text" @input="$refs.validity.validate()">
      </validity>
      <p>validation errors:</p>
      <div class="errors">
        <p v-if="validation.result.required">required username!!</p>
        <p v-if="validation.result.minleng