what is the hook name in order to alter theme function of specific element imagine that we have a list if items in $items array that it's theme function is list_item in specific page.

code is

theme('item_list', array('items' =&gt; $items));


but in my module, I want to alter the parameter 'item_list' and I want to use my custom render function 'custom_item_list'

I know that I must register and define custom_item_list function but I don't know in what hook I am able to alter the theme_function parameter of specific element.
You can use hook_theme() function to use custom item list.

Hook theme:

function mymodule_theme($existing, $type, $theme, $path)
{
  if ($type == 'module')
  {
    return array(
      'custom_item_list' =&gt; array(
        'variables' =&gt; array('var_name'=&gt;NULL),
        'template' =&gt; 'custom-item-list',
      ),
    );
  }
  return array(); //will raise fatal error if void
}


Call it as usual:

theme('custom_item_list', array('var_name' =&gt; mymodule_variable()));