[css-properties-values-api] Multiple names in @property rule

[valtlai]

Spec: https://drafts.css-houdini.org/css-properties-values-api-1/#at-property-rule

Allowing multiple custom property names in the @property rule would simplify, or make more DRY, cases where multiple very similar properties are defined:

@property <custom-property-name># {
  <declaration-list>
}

For example, the following (where --x, --y, and --z represent some coordinates):

@property --x {
  syntax: '<number>';
  inherits: false;
  initial-value: 0;
}

@property --y {
  syntax: '<number>';
  inherits: false;
  initial-value: 0;
}

@property --z {
  syntax: '<number>';
  inherits: false;
  initial-value: 0;
}

could be rewritten into:

@property --x, --y, --z {
  syntax: '<number>';
  inherits: false;
  initial-value: 0;
}

[SebastianZ]

This is already requested in w3c/css-houdini-drafts#1058 and it looks like there's already agreement in adding it.

Sebastian