Formit, require at least one of two fields

Support Extras
4

Something like this should work:

[[!FormIt?
   ...
   &customValidators=`myCustomValidator`
   &validate=`field1:myCustomValidator`
]]
<form id="myform" action="[[~[[*id]]]]#myform" method="post">   
   [[!+fi.error.field1]]
   <input type="text" name="field1" value="[[!+fi.field1]]">
   <input type="text" name="field2" value="[[!+fi.field2]]">
   ...
</form>

Snippet myCustomValidator

<?php
$success = true;
if (empty(trim($value))){ // field1 is empty
    if (isset($validator->fields["field2"])){
        if (empty(trim($validator->fields["field2"]))){ // field2 is empty
            $success = false;
        }
    } else {
        $success = false;
    }
}

if (!$success) {
    $validator->addError($key,'Please fill in either field1 or field2!');
}
return $success;