title: Determine if a string is a valid jQuery selector?
body: <p>Does jQuery have a method to determine if an argument passed to function is a selector?</p>
  
  <p>I am making a template for some jQuery plugins and I need to be able to check if the argument passed in is a jQuery selector. I want to allow for other data types and perform different methods based on what data type is passed. Detecting data types is easy, but selectors are just a string and can be constructed is many different ways.</p>
  
  <p>My goal is to create plugins that are forgiving with what you pass in for the arguments and makes educated decisions about what to do with it. Take the jQuery UI plugins for example, in some plugins, lets say we pass a callback function in the argument place holder that is for a number for a speed, it still takes the callback and runs it and uses the default for speed. That's the kind of functionality I'm going for and selectors are a pretty unique case.</p>
  
  <p>Has jQuery written a Regex for this? I couldn't find one in the code.</p>
  
  <p>If not, I guess I'll just have to write a huge Regex for this?</p>