title: How to override the html default "Please fill out this field" when validation fails in Flask?
body: <p>I have a Flask-WTF form with with <code>DataRequired</code> validators and related error messages. However, the Chrome browser seems to ignore my error messages and just displays "Please fill out this field". How do I get Flask to override this and show my messages?</p>
  
  <pre><code>from flask_wtf import FlaskForm
  from wtforms import StringField, PasswordField, SubmitField
  from wtforms.validators import DataRequired
  
  class SignupForm(FlaskForm):
      first_name = StringField('First Name', validators=[DataRequired(message='Hey, put in your first name!')])
      last_name = StringField('Last Name', validators=[DataRequired("What, you can't remember your last name?")])
      email = StringField('Email', validators=[DataRequired('Gonna need your email address!')])
      password = PasswordField('Password', validators=[DataRequired('Really need a password, Dude!')])
      submit = SubmitField('Sign Up')
  </code></pre>