Multiple wh fronting

In some languages, all wh-elements in a multiple question must be fronted.

Example
The following example is from Bulgarian:

(i) Koj kogo kakvo e pital? who whom what asked-3SG 'Who asked whom what?'

Rudin (1988) has noted that in multiple wh-fronting languages can be divided into two classes. In languages like Bulgarian, the wh-elements act like a cluster, while in languages like Czech and Polish, there seems to be a break after the first wh-element: adverbs and clitics can appear between the first wh-element and the others.

Links
Utrecht Lexicon of Linguistics