The function length should havea singular query argument.

[besok]

The test itself is not fully correct (@.* can return 1 node). Anyway, need to figure out the validation.

The test comes from RFC compliance suite

{
      "name": "functions, length, non-singular query arg",
      "selector": "$[?length(@.*)<3]",
      "invalid_selector": true,
      "tags": [
        "function",
        "length"
      ]
    },

The same check applies to
functions, length, non-singular query arg, multiple index selectors
and
functions, length, non-singular query arg, multiple name selectors

[besok]

but the test is correct. The descendant always returns a list. :(