SO in a nutshell:

"I need to do X"

"Have you tried Y?"

"No, because I don't need Y, I need X."

"Well you can do Z if you can't do Y."

"OK, sure. But how do I do X?"

"Why do you need to do X?"

(Explains why in my hyper-specific situation, I need to do X, and Y and Z won't work)

This question has been marked as a duplicate of "How to do Y"

no, this is one of the worst answers on Stack Overflow

OP had a specific question to capture opening tags. The thing OP asked about can be done with regular expressions. It is true that arbitrarily nested languages like HTML cannot generally be parsed with regular expressions, but that is not what OP asked about.

OP isn't trying to parse HTML though.... they are trying to detect opening xml tags. Which seems quite achievable with regex.

https://www.zalgo.org/

T̸̛̟͚͋͛̈̊͜͝Ờ̶̤̫̦͙̜̫͇͕͈̘̭̈̑̓̀̈́̌͊͛̆͐̌̈́͝ͅN̸̯̫̺̄̿̎͗͗́͜Y̷̢̱͚̖̤̠̞͉̅́̋̉̿̇̎̋͆͝͝ ̸̧̡̨̧̡̛̖̤̜͔̲̯̞͉͈̻̎̈̄̓̊̄́̕͘͝͠ͅT̷͎̝͌̅̔̓̒H̷̨̧̧̳̱̜͓̮͍̣̬̩̜̙͚̑̌́̑͋̽͗̎͑̊͛̍́͒̕͝͠Ḙ̵̥̥̘̻͔͛̑͒̿͋͝͝ ̶̡͚̬͈̏͌̓̔̈̔̀͌̔̓̾̓͘͝P̷͙̃́̈͐̆̂́͗̏͌̈́Ô̶͎͓̹͖̘̟̬͚̻̦̩͔͛͜͠ͅŅ̶͖̜̱͍̦̔̊͐͆̾̎́́̈́̄̓ͅẎ̸̨̭̜̼͎̜̜͕̥͙̼̤̟̞̄̊̂́ͅ ̴̡̡̛̲̟̳̯͔̝̟͙̌̽͋̏̾̆̅̏̐̅͑̿̀͒̉H̵̪̞̩̥̫̺̅̑̈́̾͌͛́̾̅̈͛͒̾̌̈͐͝Ȅ̶̘̲͙̖̬̞͕̱͍̥͈̦͈͍͔̩̑̒̐̇̑̈́̏͊̽͜͝͝͝ ̸̨̛̛̻̘̙̯̰̦̻͈͓̒̽̉̈̄̌̄͊͂̈͆ͅC̵͙̗̣̮͈̜̪̞̰̣͎̙̏̌̄͗͜Ȯ̸͇̖̼͈̗̝͔̜̘̲̦̦̾̃̆̍͝͝ͅM̷̨̧̮͕̠̘̔ͅÉ̶̡̡̢̡͕̺̗̩̝̩͇͓̄͐͆͛̔̈́̕͜ͅS̵̡͙̬͔̞̞̳͓̜͔͑̌̓̎͆͌̈͌̌̂͛̚͘͝

Calendar, remind me to ask StackOverflow tomorrow if I can ~~parse HTML with regexs~~ get someone else to do my class homework for me?

TH̘Ë͖́̉ ͠P̯͍̭O̚​N̐Y̡ H̸̡̪̯ͨ͊̽̅̾̎Ȩ̬̩̾͛ͪ̈́̀́͘ ̶̧̨̱̹̭̯ͧ̾ͬC̷̙̲̝͖ͭ̏ͥͮ͟Oͮ͏̮̪̝͍M̲̖͊̒ͪͩͬ̚̚͜Ȇ̴̟̟͙̞ͩ͌͝S̨̥̫͎̭ͯ̿̔̀ͅ

Sweet, my summoning spell worked!

So all the misery in the world is related to webdevs trying to parse html with regex?

You bastards.

I once applied to an internship for a company doing job offers aggregation. During the interview they explained to me that the core of what they did was parsing (partial) html with regex. When I asked why they wouldn't develop a custom parser, they replied to me that they were working on it, but that the internship wouldn't focus on that. I was not disappointed when it didn't get the job.

I'm not a professional code monkey although I've done a fair amount of coding, and every time I tried to do parsing myself, I later regretted it.

But telling people that they're doing it wrong is rarely met with positivity. :-)

There is a famous Erik Naggum rant about XML at, no wait, I better not link it but you can find it with a search engine if you want, which means you don't get to complain to me about it since you are the one who went looking for it. Very NSFW and VERY politically incorrect. Naggum died in 2009 but anyone who published a thing like that today would be raked over the coals.

Once you learn about parser combinators, all other parsing looks pretty dopey.

xpath <3

Using a regex on html is like eating wild mushrooms that you found in the woods. There are times where it's appropriate and safe, other times where it's completely insane and possibly deadly, and it takes considerable experience to know how to tell the difference.

Man, do gen z and alpha even know what Zalgo is?