title: Approaches to debug PHP library/vendor package code without editing library
body: <p>I use a package that's installed using <code>composer</code>.  I'm getting an error in a method in one of the package classes. I'd like to see how the values get passed around and also check a few other values inside the methods that are part of call stack.</p>
  
  <p>I could use <code>echo</code> or <code>var_dump</code> inside all those call stack methods, but I'm <em>not comfortable editing library source code</em>.</p>
  
  <p>The library uses <code>whoops</code> so I get some goodness, but it's only shows the parameters passed but I'd like to see values of certain other variables.</p>
  
  <p>Any other alternatives to this?</p>