<input type="text" list="cities">
<datalist id="cities">
<option value="北京">
<option value="上海">
<option value="廣州">
<option value="深圳">
</datalist>

<keygen name="my-key">

<form oninput="result.value=parseInt(x.value)+parseInt(y.value)">
<input type="number" id="x">+
<input type="number" id="y">=
<output name="result"></output>
</form>