Paths: $.patient.id, $.tests[*].code, $.a[0].b. Pipes: lower, upper, trim, string, number, bool, join(','), join_with('-', $.x), or($.x), default('v'), default_now(), dt('%Y%m%d'), dt_compact(), or_null(). Arrays: {"$each": "$.tests", "template": {...}}. Required: {"$required": [...]}. Escape literals with \$.