El elemento label y la accesibilidad

<label for="email">Email address</label>
<input type="email" id="email" name="email">

<!-- for="email" matches id="email" -->
<!-- Clicking "Email address" moves focus to the input -->
<!-- Required for proper accessibility -->

<!-- No for/id needed — input is inside label -->
<label>
  Email address
  <input type="email" name="email">
</label>

<!-- Works fine but explicit association is more robust
     (especially when label and input are far apart in the DOM) -->

<h2 id="section-title">Billing Details</h2>
<input type="text" name="name" aria-labelledby="section-title">
<!-- The heading serves as the accessible label for the input -->

<!-- Search form with icon button -->
<form>
  <input type="search" name="q" aria-label="Search the site">
  <button type="submit" aria-label="Submit search">
    <svg><!-- magnifier icon --></svg>
  </button>
</form>

<!-- BAD: one label for multiple inputs -->
<label>First and last name
  <input type="text" name="first">
  <input type="text" name="last">
</label>

<!-- GOOD: separate labels -->
<label for="first">First name</label>
<input type="text" id="first" name="first">

<label for="last">Last name</label>
<input type="text" id="last" name="last">

<!-- Visual + accessible required indicator -->
<label for="email">
  Email address
  <span aria-hidden="true">*</span>         <!-- visual asterisk -->
  <span class="sr-only">(required)</span>    <!-- screen reader text -->
</label>
<input type="email" id="email" name="email" required>

<fieldset>
  <legend>Shipping address</legend>

  <label for="addr-street">Street</label>
  <input type="text" id="addr-street" name="street" autocomplete="address-line1">

  <label for="addr-city">City</label>
  <input type="text" id="addr-city" name="city" autocomplete="address-level2">
</fieldset>

<fieldset>
  <legend>Preferred contact method</legend>

  <label>
    <input type="radio" name="contact" value="email"> Email
  </label>
  <label>
    <input type="radio" name="contact" value="phone"> Phone
  </label>
  <label>
    <input type="radio" name="contact" value="text"> Text message
  </label>
</fieldset>

<!-- BAD: placeholder used as a label -->
<input type="email" placeholder="Email address">
<!-- Screen readers may announce the placeholder, but many skip it -->
<!-- User cannot see the field purpose while typing -->

<!-- GOOD: -->
<label for="email">Email address</label>
<input type="email" id="email" placeholder="you@example.com">

<label for="search" class="sr-only">Search</label>
<input type="search" id="search" placeholder="Search...">

/* sr-only utility class: */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}