CacheControl header.

ContentEncoding header.

ContentLanguage header.

ContentType header.

Eq is equal constrain name.Eq(x) ⟼ Field = :value */.

Exists attribute constrain name.Exists(x) ⟼ attribute_exists(name) */.

Expires header.

Ge is greater or equal constrain name.Le(x) ⟼ Field >= :value */.

Gt is greater than constrain name.Le(x) ⟼ Field > :value */.

Is matches either Eq or NotExists if value is not defined */.

Le is less or equal constain name.Le(x) ⟼ Field <= :value */.

Lt is less than constain name.Lt(x) ⟼ Field < :value */.

Ne is non equal constrain name.Ne(x) ⟼ Field <> :value */.

NotExists attribute constrain name.NotExists(x) ⟼ attribute_not_exists(name) */.

Dyadic operation, applied over the key * value */.

Unary operation, applies over the key */.