I want to alter the input typed into the default search block in a way that when users search for "möp" (with a German umlaut) the search should be broadened to "möp OR moep" automatically.

So I simply tried to append a custom form submit to the `search_block_form` and simply expand the string by a certain logic. But then I found out that the `search_block_form` seems to be a little bit special. In *core/modules/search/src/Form/SearchBlockForm.php* I found the following comment.

> 
> 
> ```
>   /**
>    * {@inheritdoc}
>    */
>   public function submitForm(array &$form, FormStateInterface $form_state) {
>     // This form submits to the search page, so processing happens there.
>   }
> 
> ```
> 
> 

My question now is: Where do I actually add the logic exactly if not in the form submit? I don't find any redirect or controller that would help here. Could you please point me in the right direction? Or maybe, you even have a better idea than appending the logic this way?

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I removed the D8 tag as I guess the logic behind this is pretty equal amongst all common Drupal versions.