Three namespaces share this node, and the compiler keeps them strictly separate:
- `name(...)` an `@fn`, a built-in, or -- when nothing declares it -- a plain css function
- `php::name(...)` an explicitly authorized php callable ([`PhpFunctionRegistry`](https://mcp.mmoframework.fr/documentation/mmo.client/php/scs/PhpFunctionRegistry.md#phpfunctionregistry))
- `raw` calls css functions whose arguments must not be evaluated (`calc`, `clamp`, `var`, ...)