Function evaluate 

pub fn evaluate(
    surface: &AgentSurface,
    scope: &Scope<'_>,
    array_key: Option<&str>,
    has_array: bool,
    ceiling: Option<&QueryCeiling>,
) -> Result<Findings, AppError>

Decides whether surface may be applied to the envelope described by scope.

Errors

Returns AppError::Usage — exit 2 — when the request cannot be honoured as written. Every message names the offending flag and a way forward.