isIgnoredFunction = function (propertyElem, allowMap, functionWhitelist) {
  if (propertyElem && propertyElem.is('function')) {
    var funcIdent = propertyElem.first('ident');

    // allow custom properties as values
    if (funcIdent.content === 'var') {
      return true;
    }

    if (allowMap && funcIdent.content === 'map-get') {
      return true;
    }

    if (functionWhitelist.length) {
      return functionWhitelist.indexOf(funcIdent.content) !== -1;
    }
  }
  return false;
}
Checks If the property type is a function and whether it is allowed

@param {Object} propertyElem - The property element
@param {boolean} allowMap - Whether the user has specified to allow Sass function map-get
@param {Array} functionWhitelist - An array of string - function names we wish to allow
@returns {boolean} Whether the property is an ignored type or not