I've come across a form that, on the rendered page, looks like this:

```
<form id="mx_locator" name="mx_locator" method="post" action="search-results">

  <!-- form elements -->
  <span><input type="image" src="/images/search.png" onclick="loader()"></span>

</form>

```

The form itself, in the template code, looks like this:

```
{exp:mx_google_map:form result_page = "search-results" log="" lat="" unit = "" backspace="1"}
  {embed="site/sidebar_search"}
{/exp:mx_google_map:form} 

```

Question 1) Where can I edit the form html? And/or how can I add an onsubmit attribute to the form's opening tag? Does that EE code build a form tag? Or can I edit the static html elsewhere? In addition to other methods, I want to try to add an onsubmit attribute to the form tag. Not saying it's the best way, or that it'll work, but I want to try.

Question 2) How can I stop the form submission to check two text input fields before proceeding? I need to make it so **one of two fields**, in this case zip or city, are not blank. At least one must be filled. 

I thought the `loader()` bit took care of everything, meaning I could call a diff function and then have `loader()` called when the validator checks out ok, but `loader()` just handles some css changes. I have no idea how the form is calling the MXgm script or sending it data, so I don't know how to stop it or call it manually myself.

Thanks for any tips.