We have added id attributes for inputs in filter also for older templates of 1st and 2nd generation. These IDs holds unique identificator of filtering parameter.
Self-describing example below shows two filtering inputs for color and size. Attribute data-filter-code holds info about filter itself (in this case parametric filter), data-filter-id is an unique id of the filter. The id attribute is an unique id of parameter used for filtering and finally the value attribute is text value of that parameter which is displayed to customers.
<input data-url="https://step.shoptet.cz/zena/?pv30=84" data-filter-id="30" data-filter-code="pv" type="checkbox" name="pv[]" id="pv[]84" value="Bílá">
<input data-url="https://step.shoptet.cz/zena/?pv18=18" data-filter-id="18" data-filter-code="pv" type="checkbox" name="pv[]" id="pv[]18" value="S">