A file upload field that accepts multiple values:
The multiple attribute is a boolean attribute.
When present, it specifies that the user is allowed to enter more than one value in the <input> element.
Note: The multiple attribute works with the following input types: email, and file.
Tip: For <input type="file">: to select multiple files, hold down the CTRL or SHIFT key while selecting.
Tip: For <input type="email">: separate each email with a comma, like: email@example.com, firstname.lastname@example.org, email@example.com in the email field.
The numbers in the table specify the first browser version that fully supports the attribute.
The multiple attribute is new in HTML5.
In XHTML, attribute minimization is forbidden, and the multiple attribute must be defined as <input multiple="multiple" />.