formenctype [HTML5]

If the button is a submit button, this attribute specifies the type of content that is used to submit the form to the server. Possible values are:
  application/x-www-form-urlencoded: The default value if the attribute is not specified.
  multipart/form-data: Use this value if you are using an <input> element with the type attribute set to file.
  text/plain
  
If this attribute is specified, it overrides the enctype attribute of the button's form owner.
