isValidProperty = function (propertyElem) {
  if (propertyElem) {
    if (propertyElem.is('variable')) {
      return true;
    }
    else if (propertyElem.is('ident') && whitelistedValues.indexOf(propertyElem.content) !== -1) {
      return true;
    }
  }
  return false;
}
Checks If the property is of a valid type, either its a variable or it's a whitelisted ident value

@param {Object} propertyElem - The property element
@returns {boolean} Whether the property is valid or not