We would like to learn about your use case. For example, if this feature is needed to adopt Narwhals in an open source project, could you please enter the link to it below?

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Please describe the purpose of the new feature or describe the problem to solve.

Enable more alternatives to fill null values.

Suggest a solution if possible.

For the backends Pandas, Polars, and Dask, the implementation can only call the original method. For the Arrow backend, an algorithm needs to be implemented to support the limit parameter (the fill_null_backward and fill_null_forward methods do not support this parameter).

If you have tried alternatives, please describe them below.

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Additional information that may help us understand your needs.

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