The submit button will be enabled when all the form is validated. This is done by callback functions.
To specify how to validate inputs, custom attributes has been assigned to the input tags. Example:
<input type="text" name="age" id="age" required maxlength="3" size="3" mask="numeric" minlength="2">
The images indicating valid and invalid inputs are inserted into empty elements on the page:
<tr> <td>Gender:</td> <td id="_gender"></td> <td>
<input type="radio" required name="gender" value="F" id="genderFemale"> <label for="genderFemale"> Female</label>
<input required type="radio" name="gender" value="M" id="genderMale"> <label for="genderMale">Male</label></td> </tr>
Notice the id "_gender" correspond with the name of the input "gender". The "_" prefix tells the script that the validation image could be inserteded here.