Thanks, Nick

Thanks, Nick

This is the GPX parser, which might provide some insight:

L.GPX = L.FeatureGroup.extend({
initialize: function(gpx, options) {
    L.Util.setOptions(this, options);
    this._gpx = gpx;
    this._layers = {};
    
    if (gpx) {
        this.addGPX(gpx, options, this.options.async);
    }
},

loadXML: function(url, cb, options, async) {
    if (async === undefined) async = this.options.async;
    if (options === undefined) options = this.options;

    var req = new window.XMLHttpRequest();
    req.open('GET', url, async);
    try {
        req.overrideMimeType('text/xml'); // unsupported by IE
    } catch(e) {}
    req.onreadystatechange = function() {
        if (req.readyState !== 4) return;
        if(req.status === 200) cb(req.responseXML, options);
    };
    req.send(null);
},

_humanLen: function(l) {
    if (l < 2000)
        return l.toFixed(0) + ' m';
    else
        return (l/1000).toFixed(1) + ' km';
},

_polylineLen: function(line)//line is a L.Polyline()
{
    var ll = line._latlngs;
    var d = 0, p = null;
    for (var i = 0; i < ll.length; i++)
    {
        if(i && p)
            d += p.distanceTo(ll[i]);
        p = ll[i];
    }
    return d;
},

addGPX: function(url, options, async) {
    var _this = this;
    var cb = function(gpx, options) { _this._addGPX(gpx, options); };
    this.loadXML(url, cb, options, async);
},

_addGPX: function(gpx, options) {
    var layers = this.parseGPX(gpx, options);
    if (!layers) return;
    this.addLayer(layers);
    this.fire('loaded');
},  

parseGPX: function(xml, options) {
    var j, i, el, layers = [];
    var named = false, tags = [['rte','rtept'], ['trkseg','trkpt']];

    for (j = 0; j < tags.length; j++) {
        el = xml.getElementsByTagName(tags[j][0]);
        for (i = 0; i < el.length; i++) {
            var l = this.parse_trkseg(el[i], xml, options, tags[j][1]);
            for (var k = 0; k < l.length; k++) {
                if (this.parse_name(el[i], l[k])) named = true;
                layers.push(l[k]);
            }
        }
    }

    el = xml.getElementsByTagName('wpt');
    if (options.display_wpt !== false) {
        for (i = 0; i < el.length; i++) {
            var marker = this.parse_wpt(el[i], xml, options);
            if (!marker) continue;
            if (this.parse_name(el[i], marker)) named = true;
            layers.push(marker);
        }
    }

    if (!layers.length) return;
    var layer = layers[0];
    if (layers.length > 1) 
        layer = new L.FeatureGroup(layers);
    if (!named) this.parse_name(xml, layer);
    return layer;
},

parse_name: function(xml, layer) {
    var i, el, txt='', name, descr='', len=0;
    el = xml.getElementsByTagName('name');
    if (el.length)
        name = el[0].childNodes[0].nodeValue;
    el = xml.getElementsByTagName('desc');
    for (i = 0; i < el.length; i++) {
        for (var j = 0; j < el[i].childNodes.length; j++)
            descr = descr + el[i].childNodes[j].nodeValue;
    }

    if(layer instanceof L.Path)
        len = this._polylineLen(layer);

    if (name) txt += '<h2>' + name + '</h2>' + descr;
    if (len) txt += '<p>' + this._humanLen(len) + '</p>';
    
    if (layer && layer._popup === undefined) layer.bindPopup(txt);
    return txt;
},

parse_trkseg: function(line, xml, options, tag) {
    var el = line.getElementsByTagName(tag);
    if (!el.length) return [];
    var coords = [];
    for (var i = 0; i < el.length; i++) {
        var ll = new L.LatLng(el[i].getAttribute('lat'),
                    el[i].getAttribute('lon'));
        ll.meta = {};
        for (var j in el[i].childNodes) {
            var e = el[i].childNodes[j];
            if (!e.tagName) continue;
            ll.meta[e.tagName] = e.textContent;
        }
        coords.push(ll);
    }
    var l = [new L.Polyline(coords, options)];
    this.fire('addline', {line:l});
    return l;
},

parse_wpt: function(e, xml, options) {
    var m = new L.Marker(new L.LatLng(e.getAttribute('lat'),
                    e.getAttribute('lon')), options);
    this.fire('addpoint', {point:m});
    return m;
}  });

Thanks, Nick