Detailed guide on Regex

There are many incompatible regexp dialects. This describes one of the dialects, but it doesn&#x27;t even say which one.<p>It is full of errors and omissions. It&#x27;s certainly not &quot;detailed&quot;.<p>I don&#x27;t recommend this as a learning source. Sorry.

<i>&quot;Just like above example the regular expression ar[.] means: an lowercase character a, followed by letter r, followed by any character.&quot;</i><p>A period inside a character class is just a period. So that&#x27;s only going to match &quot;ar.&quot;

Haven&#x27;t read the guide, but off the bat it would benefit by at least mentioning the potential for regex with poor performance characteristics or even catastrophic backtracking, and give a few tips on how to avoid them. Neither performance nor backtracking appear in the text anywhere, nor do possessive or atomic.