In the present contribution we claim that corpus annotation serves, among other things, as an invaluable test for linguistic theories standing behind the annotation schemes, and as such represents an irreplaceable resource of linguistic information for the build-up of grammars (Sect. 1.). To support this claim we present four linguistic phenomena for the study and relevant description of which in grammar a deep layer of corpus annotation as introduced in the Prague Dependency Treebank has brought important observations, namely the information structure of the sentence (Sect. 2.), condition of projectivity and word order (Sect. 3.), types of dependency relations (Sect. 4.) and textual coreference (Sect. 5.). 1. Introductory remarks 1.1. Annotation of corpus It has been already commonly accepted in computational and corpus linguistics that grammatical (or lexicalsemantic, etc.) annotation does not ‘spoil ’ a corpus, since the annotation is done ‘in addition ’ to the raw corpus. Thus, on the contrary, annotation may and should bring an additional value to the corpus. Necessary conditions for this aim are: • its scenario is carefully (i.e. systematically and consistently) designed, and • it is based on a sound linguistic theory. This view is corroborated by the existence of annotated corpora of various languages such as Penn Treebank (English), its successors as PropBank or Penn Discourse Treebank,