:title
Test for a child

:sig
has(value : dval, key : string) bool

:params
value : value to test
key : child key

:returns
`true` when the key exists.

:content
`has(value, key)` tests for a child without creating it. It returns `false` for a missing key or a scalar.

:example capy render
var user := dval({"name": "Ada"})
print(has(user, "name"), " ", has(user, "age"), "\n")

:see-group
dval-access
