code: function validateNumber(context, name, def) {
    var value = context[name]
  
    if (value == null) {
      value = def
    }
  
    if (isNaN(value)) {
      raise(value, 'options.' + name)
    }
  
    context[name] = value
  }
docs: Validate a value to be boolean. Defaults to `def`.  Raises an exception with `context[name]` when not a boolean.