A card heading can have an optional section marked by brackets.
You can use brackets to provide spelling variants for a word, or to show that a certain morphological feature present in the source language is irrelevant in the target language.
This is equivalent to the following:
However, in the first case "превращать(ся)" will be displayed as the headword of the card.
If you have marked several headword sections as non-obligatory, the overall word list will contain every possible variant of the headword. For example, a headword written as follows: (пре)вращать(ся) will be displayed in the overall word list in four variants: превращаться, превращать, вращаться and вращать.
Important! We recommend that you do not to use brackets in headwords for any purpose other than described above.
See also:How Entries are Sorted