anchor.diff:      ===
       @debug meta.variable-exists("var1")  // false
   
  -    $var1: value 
  +    $var1: value
       @debug meta.variable-exists("var1")  // true
   
       h1
  
positive.code: <% end %>
  
  
  <% function 'meta.function-exists($name)',
              'function-exists($name)',
              returns: 'boolean' do %>
    Returns whether a function named `$name` is defined, either as a built-in
    function or a user-defined function.
  
    <% example(autogen_css: false) do %>
      @debug meta.function-exists("scale-color"); // true
      @debug meta.function-exists("add"); // false
  
  
negative.code: 
    [map function]: map
  
    <% example(autogen_css: false) do %>
      @debug meta.type-of(10px); // number
      @debug meta.type-of(10px 20px 30px); // list
      @debug meta.type-of(()); // list
  