title: Overriding validation for WTForms upon append_entry and pop_entry
body: <p>Apparently, all my fields need to have <code>DataRequired()</code> validators that is why I cant <code>append_entry()</code> and <code>pop_entry()</code> without filling them all out at first. Is there a way to override (or ignore) the validation when the user just needs to <code>append_entry()</code> or <code>pop_entry()</code> a field?</p>
  
  <p>I saw these <code>pre_validate()</code> and <code>post_validate()</code> methods in the <a href="https://wtforms.readthedocs.io/en/2.3.x/fields/#wtforms.fields.Field.pre_validate" rel="nofollow noreferrer">documentation</a> but I am having a hard time trying to understand what it does. I would appreciate if somebody would give a clear example. The document itself is also hard for me to understand.</p>