Wordpress. Set custom template for taxonomies. Change default template. template_include filter

gistfile1.php

// Add the filter
add_filter( 'template_include', 'my_custom_template');

/**
 * Returns customized templates for custom taxonomies
 *
 * @param string $template
 * @return string
 */
function my_custom_template ( $template ) {
    
    if( (is_tax('custom_tax')) 
         && is_main_query()) {
            $template =  TEMPLATEPATH . '/page-custom.php';
    } 
    
    return $template;
}