function prepareElements(JSONcontainer) {
  // cleanup the redundant svgElements;
  for (const elementType in JSONcontainer) {
    if (Object.prototype.hasOwnProperty.call(JSONcontainer, elementType)) {
      JSONcontainer[elementType].redundant = JSONcontainer[elementType].used;
      JSONcontainer[elementType].used = [];
    }
  }
}
this prepares the JSON container for allocating SVG elements
@param {object} JSONcontainer
@private