Fun project.  From examining the source code, they are using the technique that can be considered a kind of higher order abstract syntax (HOAS).  In particular, LJSON can be fooled by so called exotic terms.  E.g.<p><pre><code>  LJSON.stringify(function(v) { return v; })
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evaluates to the string<p><pre><code>  (function(v0){return v0})
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While<p><pre><code>  LJSON.stringify(function(v) { return v(null) } )
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Evaluates to the string<p><pre><code>  (function(v0){return &quot;v0&quot;})
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In the latter case, v(null) was able to examine the variable that stringify injects into the function.  In this case, v(null) is the name of the injected variable.