Allow reference to external parameter

Current expression logic allow access to attributes of the current node (or the current node itself via @). The request is to formalize access to a second object of “external parameter”, similar in spirit to the ability to parametrized jsonpath queries in PostgreSQL.

This should allow:
Employee.[?name=@param.name)) // using special node reference

Employee.[?name=param(&name)) // With a function, or

Making it much easier to construct queries with dynamic parameters. Similar to placeholders in various sql dialect