text: // Expression parser security
  //
  // Executing arbitrary expressions like enabled by the expression parser of
  // mathjs involves a risk in general. When you're using mathjs to let users
  // execute arbitrary expressions, it's good to take a moment to think about
  // possible security and stability implications, especially when running the
  // code server side.
  //
  // There is a small number of functions which yield the biggest security risk
  // in the expression parser of math.js:
  //
  // - `import` and `createUnit` which alter the built-in functionality and allow
  //   overriding existing functions and units.
  // - `eval`, `parse`, `simplify`, and `derivative` which parse arbitrary input
  //   into a manipulable expression tree.
  //
  // To make the expression parser less vulnerable whilst still supporting most
  // functionality, these functions can be disabled, as demonstrated in this
  // example.
  
  var math = require('../../index');
  var limitedEval = math.eval;
  
  math.import({
    'import':     function () { throw new Error('Function import is disabled') },
    'createUnit': function () { throw new Error('Function createUnit is disabled') },
    'eval':       function () { throw new Error('Function eval is disabled') },
    'parse':      function () { throw new Error('Function parse is disabled') },
    'simplify':   function () { throw new Error('Function simplify is disabled') },
    'derivative': function () { throw new Error('Function derivative is disabled') }
  }, {override: true});
  
  console.log(limitedEval('sqrt(16)'));     // Ok, 4
  console.log(limitedEval('parse("2+3")')); // Error: Function parse is disabled
  