How to use the npm/lib/utils/log.silly function in npm

function install_ (pkg, reg, seen, mustHave, pkglist, cb) {
  log.verbose(pkg, "install_")
  if (seen[pkg]) return cb() // repeat, skip it
  seen[pkg] = true

  // it's a local thing or a url if it has a / in it.
  if (pkg.indexOf("/") !== -1 || pkg === ".") {
    log.silly(pkg, "install local")
    return cache.add(pkg, finisher(pkg, reg, pkglist, cb))
  }

  // now we know it's not a URL or file,
  // so handle it like a tag, version, or range.
  pkg = pkg.split("@")
  var name = pkg[0]
    , defTag = npm.config.get("tag")
    , ver = pkg.slice(1).join("@").trim() || defTag
    , range = semver.validRange(ver)
    , exact = semver.valid(ver)
    , tag = !exact && !range && range !== "" && ver
  log.verbose([pkg, mustHave], "must install?")
  pkg = pkg.join("@")
  seen[name+"@"+ver] = true

function _source(pkg, reg, pkglist, cb) {
    log.verbose(pkg, "_source");

    // it's a local thing or a url if it has a / in it.
    if (pkg.indexOf("/") !== -1 || pkg === ".") {
        log.silly(pkg, "install local");
        return cache.add(pkg, finisher(pkg, reg, pkglist, cb));
    }

    // now we know it's not a URL or file,
    // so handle it like a tag, version, or range.
    pkg = pkg.split("@");
    var name = pkg[0],
        defTag = npm.config.get("tag"),
        ver = pkg.slice(1).join("@").trim() || defTag,
        range = semver.validRange(ver),
        exact = semver.valid(ver),
        tag = !exact && !range && range !== "" && ver,
        pkg = pkg.join("@");

    // at this point, assume that it has to be debianized
    if (exact) {

getData(name, function (er, data) {
    if (er) return cb(er)
    log.silly(data, pkg)
    if (tag) {
      log.verbose(tag, pkg+" tag")
      var tags = data["dist-tags"]
      if (!tags[tag]) return log.er(cb, "Tag not found: "+data.name+"@"+tag)(er)
      install_(data.name+"@"+tags[tag], reg, seen, mustHave, pkglist, cb)
    } else {
      log.verbose(tag, pkg+" range")
      // prefer the default tag version.
      var defTag = npm.config.get("tag")
        , satis
      defTag = defTag && data["dist-tags"] && data["dist-tags"][defTag]
      if (semver.satisfies(defTag, range)) satis = defTag
      else satis = semver.maxSatisfying(Object.keys(data.versions), range)

      if (!satis) return cb(new Error(
        "No satisfying version found for '"+data.name+"'@'"+range+"'"))

getData(name, function (er, data) {
        if (er) return cb(er);
        log.silly(data, pkg);
        if (tag) {
            log.verbose(tag, pkg + " tag");
            var tags = data["dist-tags"];
            if (!tags[tag]) return log.er(cb, "Tag not found: " + data.name + "@" + tag)(er);
            _source(data.name + "@" + tags[tag], reg, pkglist, cb);
        } else {
            log.verbose(tag, pkg + " range");
            // prefer the default tag version.
            var defTag = npm.config.get("tag"), satis;
            defTag = defTag && data["dist-tags"] && data["dist-tags"][defTag];
            if (semver.satisfies(defTag, range)) satis = defTag;
            else satis = semver.maxSatisfying(Object.keys(data.versions), range);

            if (!satis) return cb(new Error(
                "No satisfying version found for '" + data.name + "'@'" + range + "'"));
            _source(data.name + "@" + satis, reg, pkglist, cb);