If you are searching for a Czech or Slovak surname, be sure to try all forms, including masculine and feminine, singular and plural. In some cases, Genealogy Indexer will automatically try many forms for you. This will happen only when you have selected "Czech + Slovak" from the place drop-down menu, and you have selected "Regular Match" or "OCR-Adjusted," and your search term consists of a single word that does not end in -ov? or -ovych. For example, if you select "Czech + Slovak" and "Regular Match," and search for Novak, Genealogy Indexer will return results for Novak, Novakova, Novakovi, or Novakovy. Likewise, searches for Horacek will include Horackova. However, a search for Novakova will NOT include Novak.
The algorithm used to automatically determine variant surname forms should account for the vast majority of Czech and Slovak surnames, but it will undoubtedly miss some rare names, in which case you should search for variant forms manually. Also, note that you will have to manually search for variants if your search term consists of a surname plus a given name, or, generally, more than one word. You can include variants in a single search by separating them with the | symbol, as in Novak|Novakova.