Complexity expansions in comparisons of character sequences

This paper discusses the basic principles of the comparison of character sequences (texts of any nature of language). Examples of definitions of measures of proximity and distances between texts are given. Particular attention is paid to the relative complexity of texts: a measure generalizing the complexity approach of Lempel-Ziv for the case of pairs (groups) of texts with the addition of copying operations specific to a particular application domain. The relative complexity is compared with other known measures and examples of its use are shown.