Modifications to textpattern/include/txp_perfs.php

I've included the entire function, but the only modification was to add the 
"section_title" element to the $things array.

	function permlinkmodes($item,$var) 
	{
		$things = array(
			"messy" => gTxt('messy'),
			"id_title" => gTxt('id_title'),
			"section_id_title" => gTxt("section_id_title"),
			"section_title" => gTxt("section_title"),
			"section_category_title" => gTxt("section_category_title"),
			"year_month_day_title" => gTxt("year_month_day_title"),
			"title_only" => gTxt("title_only"),
#			"category_subcategory" => gTxt('category_subcategory')
		);
		return selectInput($item, $things, $var);
	}


//----------------------------------------------------------------------------//

Modifications to textpattern/publish/taghandlers.php

I've included the entire function, but the only modification was the addition of 
the 'section_title' case to the switch block.

	function permlinkurl($article_array) 
	{
		global $permlink_mode, $txpac;

		if (isset($txpac['custom_url_func']) and is_callable($txpac['custom_url_func']))
			return call_user_func($txpac['custom_url_func']);

		extract($article_array);
		
		if (!isset($title)) $title = $Title;
		if (empty($url_title)) $url_title = stripSpace($title);
		if (empty($section)) $section = $Section; // lame, huh?
		if (empty($posted)) $posted = $Posted;
		if (empty($thisid)) $thisid = $ID;

		if (empty($category)) {
			$Category1 = (!empty($Category1)) ? $Category1 : $category1;
			$Category2 = (!empty($Category2)) ? $Category2 : $category2;
			$category = (!empty($Category1)) ? $Category1 : $Category2;
		}

		$category = (!empty($category)) ? $category.'/' : '';
		
		switch($permlink_mode) {
			case 'section_id_title':
				return hu."$section/$thisid/$url_title";
			case 'section_title':
				return hu."$section/$url_title";
			case 'section_category_title':
				return hu."$section/{$category}{$url_title}";
			case 'year_month_day_title':
				list($y,$m,$d) = explode("-",date("Y-m-d",$posted));
				return hu."$y/$m/$d/$url_title";
			case 'id_title':
				return hu."$thisid/$url_title";	
			case 'title_only':
				return hu."$url_title";	
			case 'messy':
				return hu."?id=$thisid";	
		}
	}


//----------------------------------------------------------------------------//

Modifications to textpattern/lang/en-us.txt

I added the following line:
section_title => /section/title
section_category_title => /section/category/title