Correct syntax rules for <ident> (mdn#34340)

* Correct syntax rules for

* Update files/en-us/web/css/ident/index.md

* Update files/en-us/web/css/ident/index.md

Co-authored-by: Dipika Bhattacharya <[email protected]>

* Apply suggestions from code review

Co-authored-by: Dipika Bhattacharya <[email protected]>

* Review comments

* Update files/en-us/web/css/ident/index.md

Co-authored-by: Dipika Bhattacharya <[email protected]>

---------

Co-authored-by: Dipika Bhattacharya <[email protected]>

files/en-us/web/css/ident/index.md

@@ -2,7 +2,7 @@
 title: <ident>
 slug: Web/CSS/ident
 page-type: css-type
-spec-urls: https://drafts.csswg.org/css-values/#css-identifier
+spec-urls: https://drafts.csswg.org/css-values/#typedef-ident
 ---
 
 {{CSSRef}}
@@ -11,39 +11,54 @@ The **`<ident>`** [CSS](/en-US/docs/Web/CSS) [data type](/en-US/docs/Web/CSS/CSS
 
 ## Syntax
 
-The syntax of `<custom-ident>` is similar to CSS identifiers (such as property names), except that it is [case-sensitive](https://en.wikipedia.org/wiki/Case_sensitivity). It consists of one or more characters, where characters can be any of the following:
+A CSS identifier consists of one or more characters, which can be any of the following:
 
-- any alphabetical character (`A` to `Z`, or `a` to `z`),
-- any decimal digit (`0` to `9`),
-- a hyphen (`-`),
-- an underscore (`_`),
-- an escaped character (preceded by a backslash, `\`),
-- a [Unicode](https://en.wikipedia.org/wiki/Unicode) character (in the format of a backslash, `\`, followed by one to six hexadecimal digits, representing its Unicode code point)
+- any {{glossary("ASCII")}} character in the ranges `A-Z` and `a-z`
+- any decimal digit (`0` to `9`)
+- a hyphen (`-`)
+- an underscore (`_`)
+- any other {{glossary("Unicode")}} character `U+00A0` and higher (that is, any other non-ASCII Unicode character)
+- an [escaped character](escaping_characters)
 
-Note that `id1`, `Id1`, `iD1` and `ID1` are all different identifiers as they are [case-sensitive](https://en.wikipedia.org/wiki/Case_sensitivity). On the other hand, as there are several ways to escape a character, `toto\?` and `toto\3F` are the same identifiers.
+Additionally, an identifier must not start with an unescaped digit, and must not start with an unescaped hyphen followed by an unescaped digit.
+
+Note that `id1`, `Id1`, `iD1` and `ID1` are all different identifiers because they are [case-sensitive](https://en.wikipedia.org/wiki/Case_sensitivity). On the other hand, since there are several ways to escape a character, `toto\?` and `toto\3F` are the same identifiers.
+
+### Escaping characters
+
+Escaping a character means representing it in a way that changes how it is interpreted by a software system. In CSS, you can escape a character by adding a backslash (`\`) in front of the character. Any character, except the hexadecimal digits `0-9`, `a-f`, and `A-F`, can be escaped in this way. For example, `&` can be escaped as `\&`.
+
+You can also escape any character with a backslash followed by the character's Unicode {{glossary("code point")}} represented by one to six hexadecimal digits. For example, `&` can be escaped as `\26`. In this usage, if the escaped character is followed by a hexadecimal digit, do one of the following:
+
+- Place a space or other whitespace character after the Unicode code point.
+- Provide the full six-digit Unicode code point of the character being escaped.
+
+For example, the string `&123` can be escaped as `\26 123` (with a whitespace) or `\000026123` (with the six-digit Unicode code point for `&`) to ensure that `123` is not considered as part of the escape pattern.
 
 ## Examples
 
 ### Valid identifiers
 
 ```plain example-good
-nono79        A mix of alphanumeric characters and numbers
-ground-level  A mix of alphanumeric characters and a dash
--test         A dash followed by alphanumeric characters
---toto        A custom-property like identifier
-_internal     An underscore followed by alphanumeric characters
-\22 toto      A Unicode character followed by a sequence of alphanumeric characters
-bili\.bob     A correctly escaped period
+nono79        /* A mix of alphanumeric characters and numbers */
+ground-level  /* A mix of alphanumeric characters and a dash */
+-test         /* A hyphen followed by alphanumeric characters */
+--toto        /* A custom-property like identifier */
+_internal     /* An underscore followed by alphanumeric characters */
+\22 toto      /* An escaped character followed by alphanumeric characters */
+\000022toto   /* Same as the previous example */
+bili\.bob     /* A correctly escaped period */
+🔥123         /* A non-ASCII character followed by numbers */
 ```
 
 ### Invalid identifiers
 
 ```plain example-bad
-34rem     It must not start with a decimal digit.
--12rad    It must not start with a dash followed by a decimal digit.
-bili.bob  Only alphanumeric characters, _, and - needn't be escaped.
-'bilibob' This would be a {{CSSxRef("&lt;string&gt;")}}.
-"bilibob" This would be a {{CSSxRef("&lt;string&gt;")}}.
+34rem     /* Must not start with a decimal digit */
+-12rad    /* Must not start with a dash followed by a decimal digit */
+bili.bob  /* ASCII characters apart from alphanumerics must be escaped */
+'bilibob' /* Treated as a string */
+"bilibob" /* Treated as a string */
 ```
 
 ## Specifications