What characters/symbols are allowed within the CSS class selectors?
I know that the following characters are invalid, but what characters are valid?
~ ! # $ % ^ & * ( ) + = , . / ' ; : " ? > < [ ] \ { } | ` #
You can check directly at the CSS grammar.
Basically1, a name must begin with an underscore (_), a hyphen (-), or a letter(a–z), followed by any number of hyphens, underscores, letters, or numbers. There is a catch: if the first character is a hyphen, the second character must2 be a letter or underscore, and the name must be at least 2 characters long.
-?[_a-zA-Z]+[_a-zA-Z0-9-]*
In short, the previous rule translates to the following, extracted from the W3C specification:
In CSS, identifiers (including element names, classes, and IDs in
selectors) can contain only the characters [a-z0-9] and ISO 10646
characters U+00A0 and higher, plus the hyphen (-) and the underscore
(_); they cannot start with a digit, or a hyphen followed by a digit.
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".
Identifiers beginning with a hyphen or underscore are typically reserved for browser-specific extensions, as in -moz-opacity.
1 It's all made a bit more complicated by the inclusion of escaped Unicode characters (that no one really uses).
2 Note that, according to the grammar I linked, a rule starting with two hyphens, e.g., --indent1, is invalid. However, I'm pretty sure I've seen this in practice.
To my surprise most answers here are wrong. It turns out that:
Any character except NUL is allowed in CSS class names in CSS. (If CSS contains NUL (escaped or not), the result is undefined. [CSS-characters])
Mathias Bynens' answer links to explanation and demos showing how to use these names. Written down in CSS code, a class name may need escaping, but that doesn’t change the class name. E.g. an unnecessarily over-escaped representation will look different from other representations of that name, but it still refers to the same class name.
Most other (programming) languages don’t have that concept of escaping variable names (“identifiers”), so all representations of a variable have to look the same. This is not the case in CSS.
Note that in HTML there is no way to include space characters (space, tab, line feed, form feed and carriage return) in a class name attribute, because they already separate classes from each other.
So, if you need to turn a random string into a CSS class name: take care of NUL and space, and escape (accordingly for CSS or HTML). Done.
I’ve answered your question in-depth at CSS character escape sequences. The article also explains how to escape any character in CSS (and JavaScript), and I made a handy tool for this as well. From that page:
If you were to give an element an ID value of ~!#$%^&*()_+-=,./';:"?><[]{}|`#, the selector would look like this:
CSS:
<style>
#\~\!\#\$\%\^\&\*\(\)\_\+-\=\,\.\/\'\;\:\"\?\>\<\[\]\\\{\}\|\`\#
{
background: hotpink;
}
</style>
JavaScript:
<script>
// document.getElementById or similar
document.getElementById('~!#$%^&*()_+-=,./\';:"?><[]\\{}|`#');
// document.querySelector or similar
$('#\\~\\!\\#\\$\\%\\^\\&\\*\\(\\)\\_\\+-\\=\\,\\.\\/\\\'\\;\\:\\"\\?\\>\\<\\[\\]\\\\\\{\\}\\|\\`\\#');
</script>
Read the W3C spec. (this is CSS 2.1; find the appropriate version for your assumption of browsers)
relevant paragraph:
In CSS, identifiers (including
element names, classes, and IDs in
selectors) can contain only the
characters [a-z0-9] and ISO 10646
characters U+00A1 and higher, plus the
hyphen (-) and the underscore (_);
they cannot start with a digit, or a
hyphen followed by a digit.
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".
As #mipadi points out in Kenan Banks's answer, there's this caveat, also in the same webpage:
In CSS, identifiers may begin with '-'
(dash) or '_' (underscore). Keywords
and property names beginning with '-'
or '_' are reserved for
vendor-specific extensions. Such
vendor-specific extensions should have
one of the following formats:
'-' + vendor identifier + '-' + meaningful name
'_' + vendor identifier + '-' + meaningful name
Example(s):
For example, if XYZ organization added
a property to describe the color of
the border on the East side of the
display, they might call it
-xyz-border-east-color.
Other known examples:
-moz-box-sizing
-moz-border-radius
-wap-accesskey
An initial dash or underscore is
guaranteed never to be used in a
property or keyword by any current or
future level of CSS. Thus typical CSS
implementations may not recognize such
properties and may ignore them
according to the rules for handling
parsing errors. However, because the
initial dash or underscore is part of
the grammar, CSS 2.1 implementers
should always be able to use a
CSS-conforming parser, whether or not
they support any vendor-specific
extensions.
Authors should avoid vendor-specific
extensions
The complete regular expression is:
-?(?:[_a-z]|[\200-\377]|\\[0-9a-f]{1,6}(\r\n|[ \t\r\n\f])?|\\[^\r\n\f0-9a-f])(?:[_a-z0-9-]|[\200-\377]|\\[0-9a-f]{1,6}(\r\n|[ \t\r\n\f])?|\\[^\r\n\f0-9a-f])*
So all of your listed characters, except “-” and “_” are not allowed if used directly. But you can encode them using a backslash foo\~bar or using the Unicode notation foo\7E bar.
For those looking for a workaround, you can use an attribute selector, for instance, if your class begins with a number. Change:
.000000-8{background:url(../../images/common/000000-0.8.png);} /* DOESN'T WORK!! */
to this:
[class="000000-8"]{background:url(../../images/common/000000-0.8.png);} /* WORKS :) */
Also, if there are multiple classes, you will need to specify them in selector or use the ~= operator:
[class~="000000-8"]{background:url(../../images/common/000000-0.8.png);}
Sources:
https://benfrain.com/when-and-where-you-can-use-numbers-in-id-and-class-names/
Is there a workaround to make CSS classes with names that start with numbers valid?
https://developer.mozilla.org/en-US/docs/Web/CSS/Attribute_selectors
My understanding is that the underscore is technically valid. Check out:
https://developer.mozilla.org/en/underscores_in_class_and_id_names
"...errata to the specification published in early 2001 made underscores legal for the first time."
The article linked above says never use them, then gives a list of browsers that don't support them, all of which are, in terms of numbers of users at least, long-redundant.
I would not recommend to use anything except A-z, _- and 0-9, while it's just easier to code with those symbols. Also do not start classes with - while those classes are usually browser-specific flags. To avoid any issues with IDE autocompletion, less complexity when you may need to generate those class names with some other code for whatever reason. Maybe some transpiling software may not work, etc., etc.
Yet CSS is quite loose on this. You can use any symbol, and even emoji works.
<style>
.😭 {
border: 2px solid blue;
width: 100px;
height: 100px;
overflow: hidden;
}
</style>
<div class="😭">
😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅
</div>
We can use all characters in a class name. Even characters like # and .. We just have to escape them with \ (backslash).
.test\.123 {
color: red;
}
.test\#123 {
color: blue;
}
.test\#123 {
color: green;
}
.test\<123 {
color: brown;
}
.test\`123 {
color: purple;
}
.test\~123 {
color: tomato;
}
<div class="test.123">test.123</div>
<div class="test#123">test#123</div>
<div class="test#123">test#123</div>
<div class="test<123">test<123</div>
<div class="test`123">test`123</div>
<div class="test~123">test~123</div>
For HTML5 and CSS 3, classes and IDs can start with numbers.
Going off of Kenan Banks's answer, you can use the following two regex matches to make a string valid:
[^a-z0-9A-Z_-]
This is a reverse match that selects anything that isn't a letter, number, dash or underscore for easy removal.
^-*[0-9]+
This matches 0 or 1 dashes followed by 1 or more numbers at the beginning of a string, also for easy removal.
How I use it in PHP:
// Make alphanumeric with dashes and underscores (removes all other characters)
$class = preg_replace("/[^a-z0-9A-Z_-]/", "", $class);
// Classes only begin with an underscore or letter
$class = preg_replace("/^-*[0-9]+/", "", $class);
// Make sure the string is two or more characters long
return 2 <= strlen($class) ? $class : '';
While inspecting some part of css of facebook i've noticed some class like this "_5pcb _5tmf _5p3y _50f3". Does the underscore has any special use or just for aesthetic and readability? I'm aware that underscores and hypens are valid character but I'm just wondering if the underscore in the front has a special use
The underscore itself has no special meaning (and I don't find it very aesthetic), but you cannot start class names with a digit, so it's probably just padding for that.
Basically, a name must begin with an underscore (_), a hyphen (-), or a letter(a–z), followed by any number of hyphens, underscores, letters, or numbers. There is a catch: if the first character is a hyphen, the second character must be a letter or underscore, and the name must be at least 2 characters long.
-?[_a-zA-Z]+[_a-zA-Z0-9-]*
Note that, according to the CSS grammar, a rule starting with TWO hyphens, e.g. --className, is invalid.
I have a CSS Selectory, which identifies screen elements:
DIV[id^=WIN_][id$=_304255502]
...will find an element which starts with WIN_ and ends with _304255502
Is there an equivalent to ^ and $ which would be "contains"? eg. DIV[id*=_3042]
Thanks for any help,
Mark
As mentioned in the comments to your question, the correct answer is the instance substring matching attribute selector:
[id*=xxx]
where ‘xxx’ is the string you want to match against. This is supported by IE7+ and every other modern browser (http://www.quirksmode.org/css/selectors/).
To dive a bit deeper, if the string you’re searching for isn’t a CSS ‘identifier’ then it needs to be enclosed with quotes (either single or double). An identifier:
can contain only the characters [a-zA-Z0-9] and ISO 10646 characters U+00A0 and higher, plus the hyphen (-) and the underscore (_); they cannot start with a digit, two hyphens, or a hyphen followed by a digit.
So if the string you’re searching for doesn’t match that (which looks possible given your sample data) then you’ll have to quote it. Might not be a bad idea to do that anyway.
The validator should allow only alphabetic characters (a-z and A-Z), dots(.),comma(,), slash(/) and hyphen (-). Please help to to find out one. Or tell me how to create one customized to my specifications.
I have tried [a-zA-Z,-/.] and it works but my requirements only allow for a maximum of 1 of each of the non-letter characters I specified (.,/-).
Try: ^[A-Za-z]*[-a-zA-Z,/.]{1}[A-Za-z]*$
Explanation
^ Anchor to start of string
[A-Za-z]* may be surrounded by multiple letters
[-a-zA-Z,/.]{1} Only one of the enclosed characters
[A-Za-z]* may be surrounded by multiple letters
$ Anchor to end of string
Let's say I have
<span class="1">hello</span>
And I want to declare:
span.1 { /* rules */ }
This does not seem to work (i.e. the CSS rule is not being applied.) Is there a way to get this to work? I tried just quoting the "1" in the CSS selector but that doesn't appear to be it.
See this: Which characters are valid in CSS class names/selectors?
a (class) name must begin with an underscore (_), a dash (-), or a letter(a–z)
You should always name your classes and IDs with semantics in mind. What meaning does a number bring to anybody? What does it count?
To avoid this, having IDs and classes named as just integers isn't valid CSS according to W3, and thus not supported by most browsers. Always validate your HTML and CSS.
The solution is to simply give your class a more meaningful name. What are you counting? Is it comments on a blog? If so, you could just add the class comment to each of them. If you really need unique name for each, you could use comment5 instead, but that doesn't seem to make much sense as a class, in which case you should be using IDs instead.
The exact naming requirements is also described in W3C's CSS specification, section 4.1.3 Characters and case:
In CSS, identifiers (including element names, classes, and IDs in selectors) can contain only the characters [a-zA-Z0-9] and ISO 10646 characters U+00A0 and higher, plus the hyphen (-) and the underscore (_); they cannot start with a digit, two hyphens, or a hyphen followed by a digit. 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".
So you should check CSS Grammar
so name must begin with an underscore _ ,letter(a–z), followed by any number of dashes, underscores, letters, or numbers.
EDIT:
I recommend to you read this article Valid chars in CSS class names.
Colleague #Triptych gave us awesome answer.