revision:
When present, it specifies that the user is allowed to enter more than one value in the <input> and <select> element. Valid for the "email" and "file" input types and the <select> element, the manner by which the user opts for multiple values depends on the form control.
<input multiple>
<select multiple></select>
For <input type="file">: to select multiple files, hold down the CTRL or SHIFT key while selecting.
For <input type="email">: separate each email with a comma - like: [email protected], [email protected], [email protected] - in the email field.
Try selecting more than one file when browsing for files.
<form style="margin-left:3vw;" action="/action_page.php">
<label for="files">Select files:</label>
<input type="file" id="files" name="files" multiple><br><br>
<input type="submit">
</form>
Hold down the Ctrl (windows) or Command (Mac) button to select multiple options.
<form style="margin-left:3vw;" action="/action_page.php">
<label for="cars">Choose a car:</label>
<select name="cars" id="cars" multiple>
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="opel">Opel</option>
<option value="audi">Audi</option>
</select>
<br><br>
<input type="submit" value="Submit">
</form>