Hi @Indiroy
You have addressed quite a few issues here. Just to answer a part of your question from post scriptum, a regex (regular expression) is a sequence of characters that define a search pattern (usually this pattern is used by string searching algorithms for “find” or “find and replace” operations on strings, or for input validation (quoting after Wikipedia). In practice, you can find out more and test this e.g. on the websites like the ones below (but surely, you can google much much more than that):
One of the applications of regex can be found e.g. in here: