diff --git a/bwa-typeHLA.js b/bwa-typeHLA.js
index da9ca28..5561952 100644
--- a/bwa-typeHLA.js
+++ b/bwa-typeHLA.js
@@ -1,6 +1,72 @@
-var fuzzy = 3, min_qal = 100, drop_thres = 7;
+/*****************************************************************
+ * The K8 Javascript interpreter is required to run this script. *
+ *                                                               *
+ *   Source code: https://github.com/attractivechaos/k8          *
+ *   Binary: http://sourceforge.net/projects/lh3/files/k8/       *
+ *****************************************************************/
 
-var file = arguments.length == 0? new File () : new File(arguments[0]);
+var getopt = function(args, ostr) {
+	var oli; // option letter list index
+	if (typeof(getopt.place) == 'undefined')
+		getopt.ind = 0, getopt.arg = null, getopt.place = -1;
+	if (getopt.place == -1) { // update scanning pointer
+		if (getopt.ind >= args.length || args[getopt.ind].charAt(getopt.place = 0) != '-') {
+			getopt.place = -1;
+			return null;
+		}
+		if (getopt.place + 1 < args[getopt.ind].length && args[getopt.ind].charAt(++getopt.place) == '-') { // found "--"
+			++getopt.ind;
+			getopt.place = -1;
+			return null;
+		}
+	}
+	var optopt = args[getopt.ind].charAt(getopt.place++); // character checked for validity
+	if (optopt == ':' || (oli = ostr.indexOf(optopt)) < 0) {
+		if (optopt == '-') return null; //  if the user didn't specify '-' as an option, assume it means null.
+		if (getopt.place < 0) ++getopt.ind;
+		return '?';
+	}
+	if (oli+1 >= ostr.length || ostr.charAt(++oli) != ':') { // don't need argument
+		getopt.arg = null;
+		if (getopt.place < 0 || getopt.place >= args[getopt.ind].length) ++getopt.ind, getopt.place = -1;
+	} else { // need an argument
+		if (getopt.place >= 0 && getopt.place < args[getopt.ind].length)
+			getopt.arg = args[getopt.ind].substr(getopt.place);
+		else if (args.length <= ++getopt.ind) { // no arg
+			getopt.place = -1;
+			if (ostr.length > 0 && ostr.charAt(0) == ':') return ':';
+			return '?';
+		} else getopt.arg = args[getopt.ind]; // white space
+		getopt.place = -1;
+		++getopt.ind;
+	}
+	return optopt;
+}
+
+/*********************
+ *** Main function ***
+ *********************/
+
+var c, fuzzy = 1, min_qal = 100, drop_thres = 7;
+
+// parse command line options
+while ((c = getopt(arguments, "f:m:d:")) != null) {
+	if (c == 'f') fuzzy = parseInt(getopt.arg);
+	else if (c == 'm') min_qal = parseInt(getopt.arg);
+	else if (c == 'd') drop_thres = parseInt(getopt.arg);
+}
+if (arguments.length == getopt.ind) {
+	print("");
+	print("Usage:   k8 bwa-typeHLA.js [options] <HLA-to-contig.sam>\n");
+	print("Options: -d INT     drop a contig if the edit distance to the closest gene is >INT ["+drop_thres+"]");
+	print("         -m INT     ignore a hit if the gene sequence in the alignment is <INT ["+min_qal+"]");
+	print("         -f INT     output genotypes whose edit distance is within INT from the best ["+fuzzy+"]");
+	print("");
+	exit(1);
+}
+
+// read alignments
+var file = new File(arguments[getopt.ind]);
 var buf = new Bytes();
 var re_cigar = /(\d+)([MIDSH])/g;
 
@@ -8,11 +74,13 @@ var len = {}, list = [], gcnt = [];
 while (file.readline(buf) >= 0) {
 	var m, mm, line = buf.toString();
 	var t = line.split("\t");
+	// SAM header
 	if (t[0].charAt(0) == '@') {
 		if (t[0] == '@SQ' && (m = /LN:(\d+)/.exec(line)) != null && (mm = /SN:(\S+)/.exec(line)) != null)
 			len[mm[1]] = parseInt(m[1]);
 		continue;
 	}
+	// parse gene name and exon number
 	var gene = null, exon = null;
 	if ((m = /^(HLA-[^\s_]+)_(\d+)/.exec(t[0])) != null) {
 		gene = m[1], exon = parseInt(m[2]) - 1;
@@ -20,6 +88,7 @@ while (file.readline(buf) >= 0) {
 		gcnt[exon][gene] = true;
 	}
 	if (gene == null || exon == null || t[2] == '*') continue;
+	// parse clipping and aligned length
 	var x = 0, ts = parseInt(t[3]) - 1, te = ts, clip = [0, 0];
 	while ((m = re_cigar.exec(t[5])) != null) {
 		var l = parseInt(m[1]);
@@ -33,16 +102,17 @@ while (file.readline(buf) >= 0) {
 	var left  = ts < clip[0]? ts : clip[0];
 	var right = tl - te < clip[1]? tl - te : clip[1];
 	var nm = (m = /\tNM:i:(\d+)/.exec(line)) != null? parseInt(m[1]) : 0;
-	list.push([t[2], gene, exon, ts, te, nm, left + right]);
+	list.push([t[2], gene, exon, ts, te, nm, left + right]); // left+right should be 0 given a prefix-suffix alignment
 }
 
 buf.destroy();
 file.close();
 
-// identify the primary exon(s)
+// identify the primary exons, the exons associated with most genes
 var pri_exon = [], n_pri_exons;
 {
 	var cnt = [], max = 0;
+	// count the number of genes per exon and track the max
 	for (var e = 0; e < gcnt.length; ++e) {
 		if (gcnt[e] != null) {
 			var c = 0, h = gcnt[e];
@@ -51,6 +121,7 @@ var pri_exon = [], n_pri_exons;
 			max = max > c? max : c;
 		} else cnt[e] = 0;
 	}
+	// find primary exons
 	var pri_list = [];
 	for (var e = 0; e < cnt.length; ++e) {
 		if (cnt[e] == max) pri_list.push(e + 1);
@@ -76,7 +147,7 @@ for (var i = 0; i < list.length; ++i) {
 	elist[g][list[i][2]] = true;
 }
 
-// change to the per-exon representation
+// reorganize hits to exons
 var exons = [];
 for (var i = 0; i < list.length; ++i) {
 	var li = list[i];
@@ -94,10 +165,9 @@ for (var i = 0; i < glist.length; ++i) {
 
 // type each exon
 for (var e = 0; e < exons.length; ++e) {
-//for (var e = 1; e < 3; ++e) {
 	if (exons[e] == null) continue;
 	var ee = exons[e];
-	// find good contigs and alleles that have good matches
+	// find contigs and genes associated with the current exon
 	var ch = {}, gh = {};
 	for (var i = 0; i < ee.length; ++i) {
 		if (elist[ee[i][1]][e] != null)
@@ -108,7 +178,7 @@ for (var e = 0; e < exons.length; ++e) {
 	for (var g in gh) ga.push(parseInt(g));
 	var named_ca = [];
 	for (var i = 0; i < ca.length; ++i) named_ca.push(clist[ca[i]]);
-	warn("Processing exon "+(e+1)+" (" +ga.length+ " genes; " +ca.length+ " contigs: [" +named_ca.join(",")+ "])...");
+	warn("Processing exon "+(e+1)+" (" +ga.length+ " genes; " +ca.length+ " contigs: [" +named_ca.join(", ")+ "])...");
 	// convert representation again
 	var sc = [];
 	for (var i = 0; i < ee.length; ++i) {