[html] placeholder required autocomplete

값이 비어있을 때 보여주는 값 placeholder
<input name="username" placeholder="이메일 또는 휴대전화">


input::placeholder {
  color: #dddddd;
}


반드시 입력해야 하는 값 required
<input name="email" type="email" required>


자동 완성 autocomplete

<input name="search" type="text" autocomplete="on">

<input name="email" type="email" autocomplete="email">
<input name="telephone" autocomplete="tel">


https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/autocomplete