Searches for, or replace a pattern in an input text.
A regular expression, regex or regexp is, in theoretical computer science and formal language theory, a sequence of characters that define a search pattern.
Regular expressions can be thought as a generalization of the wildcards, which you are probably familiar with their notations such as *.txt to find all text files in a file manager. The regex equivalent is ^.*\.txt$.
With NumXL functions, you can do all sort of search/replace of text in Excel using regex patterns. Furthermore, you may break down (aka tokenize) your long text into chunks based on a separator pattern.