Data from the form can come from user input from the various HTML input elements (textboxes, buttons, dropdowns, radio buttons, etc), or from data embedded in the HTML document by the server using hidden form elements, like this:

<form>
  <input type="hidden" name="var1" value="val1">
  <input type="hidden" name="var2" value="val2">
  <!-- ... -->
</form>
[download]