1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
# Syntaxes
[data](https://github.com/mdn/data/blob/main/css/syntaxes.json) |
[schema](https://github.com/mdn/data/blob/main/css/syntaxes.schema.json)
[CSS value definition syntax](https://developer.mozilla.org/en-US/docs/Web/CSS/Value_definition_syntax) is used for the formal syntax of CSS properties. The syntaxes.json file defines many of these CSS syntaxes.
For example, the `background-attachment` property has the following syntax where `<attachment>` is referring to a syntax that is defined in syntaxes.json.
Definition of `background-attachment` in properties.json:
```json
"background-attachment": {
"syntax": "<attachment>#"
}
```
Definition of `<attachment>` in syntaxes.json:
```json
"attachment": {
"syntax": "scroll | fixed | local"
},
```
CSS syntaxes might be more complex than just keywords separated by a pipe (`|`). For example, the syntax might contain values that are referencing
[CSS types](https://github.com/mdn/data/blob/main/css/types.md):
```json
"alpha-value": {
"syntax": "<number> | <percentage>"
},
```
Or, syntaxes might reference other syntaxes that are also defined in syntaxes.json:
```json
"length-percentage": {
"syntax": "<length> | <percentage>"
},
```
For more information about the formal grammar of CSS syntaxes, see [CSS value definition syntax](https://developer.mozilla.org/en-US/docs/Web/CSS/Value_definition_syntax).
|
