Syntaxes

data | schema

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:

"background-attachment": {
  "syntax": "<attachment>#"
}

Definition of <attachment> in syntaxes.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:

"alpha-value": {
  "syntax": "<number> | <percentage>"
},

Or, syntaxes might reference other syntaxes that are also defined in syntaxes.json:

"length-percentage": {
  "syntax": "<length> | <percentage>"
},

For more information about the formal grammar of CSS syntaxes, see CSS value definition syntax.