Click here for an example of part-of-speech annotation.
Part-of-speech annotation was one of the first types of annotation to be formed on corpora and is the most common today. One reason for this is because it is a task that can be carried out to a high degree of accuracy by a computer. Greene and Rubin (1971) achieved a 71% accuracy rate of correctly tagged words with their early part-of-speech tagging program (TAGGIT). In the early 1980s the UCREL team at Lancaster University reported a success rate of 95% using their program CLAWS.
Read about idiomatic tags and the tagging of contracted forms in Corpus Linguistics, chapter 2, pages 40-42.