Extexp is a text processing system. The required action is defined by a user created sequence of commands, so providing a flexible customisable tool.
Typical use cases for the tool are:
Creation of PDF documents: creation of books or reports from the markdown sources.
Creation of HTML websites: creation of web pages built from a combination of sources (typically markdown, HTML templates, HTML fragments and parameters).
The tool is not restricted to these use cases, but these are examples of current usage.