Noob here, struggling with theme.inc overrides.

So I want menus to output in a custom way. Rather than

<ul attributes >
    <li attributes >
       <a href="foo">foo</a>
    </li>
    <li attributes >
       <a href="bar">bar</a>
    </li>
 </ul>

this

<nav attributes>
   <a attributes href="foo">foo</a>
   <a attributes href="bar">bar</a>
</nav>

So I put in my theme's template.php file the following function, (my theme is called mFAC):

function mFAC_links($variables) {
    // custom stuff
}

I am starting with a light alteration, but nothing seems to have any effect. And yes I cleared the cache. Is there something I am missing.

So I want menus to output in a custom way. I would not output the following HTML.

<ul attributes>
    <li attributes>
       <a href="foo">foo</a>
    </li>
    <li attributes>
       <a href="bar">bar</a>
    </li>
 </ul>

I would replace it with the following one.

<nav attributes>
   <a attributes href="foo">foo</a>
   <a attributes href="bar">bar</a>
</nav>

So I put in the template.php file the following function (my theme is called mFAC).

function mFAC_links($variables) {
    // custom stuff
}

I am starting with a light alteration, but nothing seems to have any effect. I cleared the cache. 

Is there anything I am missing?