@stefan

I completely understand your comment with respect to "based on many years of experience and the React concept, we allow many of the components can be customized or directly replaced with a custom alternative." And you're right, this is one of the most wonderful things about React.

I struggle to understand the difficulty, however, in providing such a feature. As of v5.5.0-dev.202207010714, line 730 of Grid.tsx determines whether or not a column is sorted and this is applied in line 758, adding the class name `k-sorted`. Could something very similarly-simple not be done to determine whether or not a filter is being applied to the column and, hence, adding a `k-filtered` class?

You don't have to answer in technical detail - I'm really mentioning as food for thought and to hopefully prod Telerik in your promise to "keep an eye for an option to apply an visual indication that the filter is applied and keep the customization."

We have followed the example that @michael mentions (https://www.telerik.com/kendo-react-ui/components/grid/columns/column-menu/#toc-styling-the-column-menu-icon), but this is definitely not ideal. For every column of every grid, we'd need to determine if the column is filtered and apply our own class name using the `headerClassName` prop of the `GridColumn` component.

1. That sizes up to being a lot of repetitive work for our Developers
2. We are limited to using the pseudo CSS selector `:after` to "inject" our filtered indicator icon. In the aforementioned spirit of React, it would be much more beneficial to utilize a `span` DOM element in the same approach as the sorted column indicator.

Our other recourse is to provide overrides/extensions to the Kendo-provided `GridHeaderCell`, `GridColumn` and (possibly) `Grid` components to implement what, we feel, is basic-level functionality. As you can understand, this would create a maintainability issue for us in that for every new release of KendoReact, we'd have to update our overrides/extensions. While doing so would push more of the "cost" up front (making it easier on our Developers by requiring they use the overridden `GridColumn`, let's say), we do not want our implementation to be so "fragile" and disconnected from the KendoReact baseline (that we are paying for).

Please heavily consider imparting the "column is filtered" indicator icon functionality to within the KendoReact `Grid` component. Such has already been done for the sorted indicator and it seems only natural to have the same exist for filtering.

Thank you,

R. J. Lewis III

Actually it appears you already have this:

https://www.telerik.com/kendo-react-ui/components/grid/columns/column-menu/#toc-styling-the-column-menu-icon