docs: function runtimeRequire(mod, at, tryLink, logLevel, cb) {
  	if (typeof cb !== 'function') {
  		throw new Error('Invlaid callback: ' + cb);
  	}
  	try {
  		return cb(require(mod));
  	} catch (e) {
  		// consume
  	}
  	var modf = mod + (at ? '@' + at : '');
  	rbot.log.verbose('attempting to ' + (tryLink ? 'link/' : '') + 'install ' + modf);
  	var npm = require('npm');
  	npm.load({
  		save : false,
  		loglevel : logLevel || 'silent'
  	}, function npmLoaded(e) {
  		if (e) {
  			return cb(null, e);
  		}
  		if (tryLink) {
  			npm.commands.link([ mod ], function npmLinkCb(e) {
  				if (e) {
  					rbot.log.verbose('unable to "npm link ' + mod + '" Reason: ' + e.message);
  					return install();
  				}
  				if (semver.valid(at)) {
  					var pth = require('path').join(require.resolve(mod), '..', 'package.json');
  					rbot.log.verbose('looking for ' + pth);
  					var npmpkg = null;
  					try {
  						npmpkg = require(pth);
  					} catch (e2) {
  						rbot.log.verbose('no package.json found under ' + pth + ' Reason: ' + e2.message);
  						return install();
  					}
  					if (!semver.satisfies(npmpkg.version, at)) {
  						rbot.log.verbose('linked ' + mod + '@' + npmpkg.version
  								+ ' does not match the expected version: ' + at);
  						return install();
  					}
  				}
  				cb(require(mod));
  			});
  		} else {
  			install();
  		}
  	});
  	function install() {
  		npm.commands.install([ modf ], function npmInstallCb(e) {
  			cb(e ? null : require(mod), e);
  		});
  	}
  }