function smd_addQSVar($url, $key, $value) {
	$url = smd_removeQSVar($url, $key);
	if (strpos($url, '?') === false) {
		return ($url . '?' . $key . '=' . $value);
	} else {
		return ($url . '&' . $key . '=' . $value);
	}
}
function smd_removeQSVar($url, $key) {
	$url = preg_replace('/(.*)(\?|&)' . $key . '=[^&]+?(&)(.*)/i', '$1$2$4', $url . '&');
	$url = substr($url, 0, -1);
	return ($url);
}

// return a list of categories under (and including) the given parent category
function smd_getSubCats($parent,$cattype) {
	$parent = doSlash($parent);
	$lextrem = 1; $rextrem = 1;
	extract(safe_row("lft as lextrem, rgt as rextrem", "txp_category", "name='$parent' and type = '$cattype'"));
	$rs = safe_rows_start("id,name,title","txp_category", "lft between $lextrem and $rextrem and type = '$cattype' order by lft asc");
	$cats = array();

	while ($row = nextRow($rs)) {
		$cats[] = array(
			'id' => $row['id'],
			'name' => $row['name'],
			'title' => $row['title']
		);
	}
	return $cats;
}

// Searches the passed $str for predetermined sequences of characters
// and, if that sequence is in $allowed, replaces it as follows:
//  ?c = current global category (!c = not current category)
//  ?s = current section (!s = not current section)
//  ?t = current article title (!t = not current title)
//  ?id = current article ID, prepended with $idprefix (!id = not current ID)
//  ?field = contents of the current article's field (could be a comma-separated list)
//  !field = not the contents of the current article's field (could be a comma-separated list)
// Anything else is returned verbatim.
// Outputs two arrays; the 1st containing items for inclusion, the 2nd for exclusion
function smd_getAtts($str, $allowed, $idprefix="") {
	global $pretext, $thisarticle;

	$out = array();
	$subout = array();
	$notout = array();
	$matches = preg_split('/[,\s]+/',$str,-1,PREG_SPLIT_NO_EMPTY);

	for ($idx = 0; $idx < count($matches); $idx++) {
		$thismatch = $matches[$idx];
		if (($thismatch === "?c") && in_array("?c",$allowed)) {
			// Use global article category, if it exists
			if ($pretext['c'] != "") {
				if (!in_array($pretext['c'], $out)) {
					$out[] = $pretext['c'];
				}
			}
		} else if (($thismatch === "!c") && in_array("!c",$allowed)) {
			// Don't use global article category
			if ($pretext['c'] != "") {
				if (!in_array($pretext['c'], $notout)) {
					$notout[] = $pretext['c'];
				}
			}
		} else if (($thismatch === "?s") && in_array("?s",$allowed)) {
			// Use article section
			if ($pretext['s'] != "") {
				if (!in_array($pretext['s'], $out)) {
					$out[] = $pretext['s'];
				}
			}
		} else if (($thismatch === "!s") && in_array("!s",$allowed)) {
			// Don't use article section
			if ($pretext['s'] != "") {
				if (!in_array($pretext['s'], $notout)) {
					$notout[] = $pretext['s'];
				}
			}
		} else if (($thismatch === "?t") && in_array("?t",$allowed)) {
			// Use article URL title if this is an article.
			// It's an article if the next_id attribute exists
			if (array_key_exists('next_id',$pretext)) {
				if ($thisarticle['url_title'] != "") {
					if (!in_array($thisarticle['url_title'], $out)) {
						$out[] = $thisarticle['url_title'];
					}
				}
			}
		} else if (($thismatch === "!t") && in_array("!t",$allowed)) {
			// Don't use article URL title
			if (array_key_exists('next_id',$pretext)) {
				if ($thisarticle['url_title'] != "") {
					if (!in_array($thisarticle['url_title'], $notout)) {
						$notout[] = $thisarticle['url_title'];
					}
				}
			}
		} else if (($thismatch === "?id") && in_array("?id",$allowed)) {
			// Use article ID, prepended with $idprefix
			if (array_key_exists('next_id',$pretext)) {
				if (!in_array($idprefix . $pretext['id'], $out)) {
					$out[] = $idprefix . $pretext['id'];
				}
			}
		} else if (($thismatch === "!id") && in_array("!id",$allowed)) {
			// Don't use article ID
			if (array_key_exists('next_id',$pretext)) {
				if (!in_array($idprefix . $pretext['id'], $notout)) {
					$notout[] = $idprefix . $pretext['id'];
				}
			}
		} else if (($thismatch[0] === "?") && in_array("?field",$allowed)) {
			// Use the given field name; which may be a comma-separated sublist.
			// Split off the field name from the question mark
			$fieldname = substr($thismatch,1);
			if (array_key_exists('next_id',$pretext)) {  // Check this is an article
				if (isset($thisarticle[$fieldname])) {
					$fieldContents = $thisarticle[$fieldname];
				} else {
					$fieldContents = $fieldname;
				}
			} else {
				$fieldContents = $fieldname;
			}

			if (!empty($fieldContents)) {
				$subout = preg_split('/[,\s]+/', strip_tags($fieldContents), -1, PREG_SPLIT_NO_EMPTY);
				foreach ($subout as $subname) {
					if (!in_array($subname, $out)) {
						$out[] = $subname;
					}
				}
			}
		} else if (($thismatch[0] === "!") && in_array("!field",$allowed)) {
			// Negation. May either be a field name (and maybe another CSL) or a fixed term.
			// Split off the name from the exclamation mark
			$fieldname = substr($thismatch,1);
			if (array_key_exists('next_id',$pretext)) {  // Check this is an article
				if (isset($thisarticle[$fieldname])) {
					$fieldContents = $thisarticle[$fieldname];
				} else {
					$fieldContents = $fieldname;
				}
			} else {
				$fieldContents = $fieldname;
			}

			if (!empty($fieldContents)) {
				$subout = preg_split('/[,\s]+/', strip_tags($fieldContents), -1, PREG_SPLIT_NO_EMPTY);
				foreach ($subout as $subname) {
					if (!in_array($subname, $notout)) {
						$notout[] = $subname;
					}
				}
			}
		} else {
			if (!in_array($thismatch, $out)) {
				$out[] = $thismatch;
			}
		}
	}

	return array($out,$notout);
}