There are existing plugins that can do this. For example, this one: https://extensions.joomla.org/extensions/extension/access-a-security/site-access/registration-validation-pro/. (there are probably others, but I already know about that one and I didn't have time to search too deeply)

Did you noticed that plugin has not been updated for almost 2 years? Not to mention that it is a Paid Download one.

I think the Joomla core SHOULD put some restriction on the "username" field at least, because users can NOT edit the "username" value after registration, but they can edit "Name" and "Email". In order to avoid "weird" usernames, there MUST be some rules on it.

Thank you.

+1

I haven't modified the Joomla core, but I have written a plugin for you that should do what you want.

Please see https://github.com/Spudley/plg_user_restrictusername

Have tested it locally, but it could probably use a bit more testing. I don't have time for that right now, but thought I should let you take a look anyway.

Let me know what you think. Hopefully it meets your needs.

This is not a bug or issue - this is a feature request right?

@PhilETaylor that's how I interpreted it.

Yep, sounds like a feature request.

You can use neary ANY character in "username" and "Name" field;

This are the rules:

No space at beginning or end, at least 2 characters and must not contain the following characters: < > \ " ' % ; ( ) &.

You can't change that behavior without massive b/c issues.. and the usernames are working, so i see no issue..

You can not input a "Name" longer than 20 (or 30) characters;

The hard limit is 400 (in the database column).. You don't know how long names get, maybe some one uses are company name or url in there.. Changing this behavior would also be b/c..

You can use ANY email address!

There are millions of valid mail ru users ;)

What you are asking for is in my opinion nothing for core.. If you need customization you can use 3rd party plugins etc.

@baijianpeng @yvesh as of 3.7 any text field can have a pattern which the validator will check against it, according to #13094. The missing link here for fully customisable form fields is a way to override the fields properties similar to the layouts. I know @phproberto has some working code for this, so I'm kindly asking him to make a PR

Spamming is really getting out of hand

@martinlines Activate the inbuilt Captcha and try see what happens. You will be positively surpriced how well it works on the issue you see ;)

@martinlines Please ask help on the forums. This repository concerns in first Place Joomla-Core coding, thanks.

I'm closing this issue as it is not something we will do in core.
Also there are already existing solutions both in core (captcha) and 3rd party (spam control extensions) which will help with the original issue.