Its quite a simple but in my opinion weird problem i basically have this regex and entered a few tests and they work.
(?=^\*)|(?=^.{1,254}$)(^(?:(?!\d+\.)[a-zA-Z0-9_\-\{\}]{1,63}\.?)+(?:[a-zA-Z\{\}]{1,})$)
https://regex101.com/r/hU6tP0/2
But when i try to use it in html it fails. But if i test it in javascript it works.
http://jsfiddle.net/ek6kby2q/9/
I don't have much knowledge at all about regex so maybe anyone know whats going wrong or got any tips to make the regex better is welcome.
As an html attribute, the pattern must match all the string from the beginning to the end, that's why (?=^\*) fails to do it, since it matches zero characters.
Use this pattern instead:
\*.*|(?!.{255})(?:[A-Za-z_{}-][\w{}-]{0,62}\.?)+[A-Za-z{}]+
(You can omit the anchors since they are implicit)
*.com but for example this doesn't *<com> or *!com! In any case i will select your answer because i now understand why it doesn't work.*<com> and *!com! in your fiddle and it works too. If you don't want to validate these two cases, replace .* with something more explicit.\*.*| should be changed so the regex says something like: The beginning of the string can be a * but the rest should still follow the current regex in my original post - \*.*| Instead of what it says now. if its starts with a * then ignore the entire regex(?!.{255})(?:\*|(?:\*\.)?(?:[A-Za-z_{}-][\w{}-]{0,62}\.?)+[A-Za-z{}]+) that allows a single * or all the subpattern starting with an optional *. (if you don't need the dot, replace (?:\*\.)? with \*?)