??

that should mean that escaped characters should be allowed as class names.
However, escaping the @ still yields the same error

Forgive me for not being a mind reader.

@brianteeman github did this automatically... sorry

Steps to reproduce the issue

try to add uk-visible@m as link class to any menu item

Expected result

uk-visible@m should be stored

Actual result

class name value throws error Invalid field: Link Class

System information (as much as possible)

j4.1.2

a css clsass with @ in the name is invalid. Doesnt matter what you escape it with it is not valid.

Just try it with a basic html page and you will see it doess not work

https://codepen.io/brianteeman/pen/WNdgNmO

If you write the classes with a escape, it works
.re\@d { color: red; } .uk-visible\@m { color: pink; }

I tried directly in the browser, I inserted a class with @ on an element and created the css definition, the browser added automatically the \ symbol

a css clsass with @ in the name is invalid. Doesnt matter what you escape it with it is not valid.

Just try it with a basic html page and you will see it doess not work

the w3 reference seems to talk about @ within a css file not as a class name in html

A class name with a @, escaped or not, in a HTML5 Class attribute is not permitted.
So you can't insert in a "class" field (for example a menu link class) in Joomla because it isn't a field that generate some CSS, but it fills an HTML Class attribute in the HTML source.

Ex:
<span class="red@2">NOT PERMITTED</span>

A class name with a @, escaped or not, in a HTML5 Class attribute is not permitted. So you can't insert in a "class" field (for example a menu link class) in Joomla because it isn't a field that generate some CSS, but it fills an HTML Class attribute in the HTML source.

Ex: <span class="red@2">NOT PERMITTED</span>
@simbus82 this is directly described in the w3 doc which @brianteeman referred me to. and it specificaly states that

Identifiers can also contain escaped characters and any ISO 10646 character as a numeric code (see next item). For instance, the identifier "B&W?" may be written as "B&W?" or "B\26 W\3F".

source: https://www.w3.org/TR/CSS21/syndata.html#characters

so did you try with a numeric code

@brianteeman yup. same error
apparently it strips everything not alphanumeric

Not suprised - just wanted to be ceertain.

I personally still say it should not be valid to use an @ in the name of a class but I guess if someone is able to modify the cssvalidation rule in a secure way then it could be fixed.

Doesnt seem even a low priority

@brianteeman totally agree on the priority level.

Can be closed see #41332

please test #41332