Regex constructor block

Block regex constructor allows you to easily construct regular expression using several tools, that visualise expression you wrote, describe and test it.
This block allows you to create regular expression using several tools:
syntax tree  shows you the inner structure of regular expressions;
explaining graph  shows you how your expression will work in a graphical way;
description  formulates the meaning of your expression in English;
testing tool  allows you to enter strings and see how they match your regex.
You can also select a part of you expression and see corresponding parts selected in all tools (testing included!).
This block may be useful if you teachers or students have to write regexes working on the course.