Example
$form = new Form('plugins-passfield-form-1', 'horizontal');
$form->addHelper('<span class="help-block">password must contain lowercase + uppercase letters and be 6 characters long</span>', 'user-passfield');
$form->addInput('password', 'user-passfield', '', 'password', 'autocomplete=new-password, required=required');
$form->addPlugin('passfield', '#user-passfield', 'lower-upper-min-6');
<div class="row mb-3">
<label for="user-passfield" class="col-sm-4 col-form-label">
password <sup class="text-danger">* </sup>
</label>
<div class="col-sm-8">
<input id="user-passfield" name="user-passfield" type="password" value="" aria-describedby="user-passfield-helper" autocomplete="new-password" required="required" class="form-control">
<span class="form-text" id="user-passfield-helper"><span class="help-block">
password must contain lowercase + uppercase letters and be 6 characters long</span></span>
</div>
</div>