There follows a brief description of the Basic Tagset used for word class annotation of the whole of the British National Corpus. The list is extracted from a larger document, A users guide to the Grammatical Tagging of the BNC , a draft of which is also available. Each tag consists of three characters. Generally, the first two characters indicate the general part of speech, and the third character is used to indicate a subcategory. When the most general, unmarked category of a part of speech is indicated, in general the third character is 0.
Some theories treat that here as a relative pronoun, whereas others treat it as a conjunction.
N.B. The ORD tag is used whether these words are used in a nominal or in an adverbial role. The preposition of . Because of its frequency and its almost exclusively postnominal function, of is assigned a special tag of its own. TO0 Infinitive marker to UNC Unclassified items which are not appropriately classified as items of the English lexicon.