This page describes currently proposed language for meta-descriptions. It may be updated frequently. = Relational operators = Standard relational operators apply ||Meaning || Operator || ||Less than ||< || ||Less or equal ||<= || ||Greater than ||> || ||Greater or equal||>= || ||Equal ||== || ||Different than ||!= || = Logical operators = Standard logical operators apply ||Meaning || Operator || ||And || and || ||Or || or || ||Xor || xor || ||Not || not || For events in the timeline of events, using ''and'' or ''or'' operators denotes that any ordering between these events is possible. = Arithmetic operators = Standard arithmetic operators apply and parenthesis are used for non-obvious precedence = Temporal operators = We want to be able to denote order and concurrency of events and state changes, and duration of events. ||Meaning || Operator and example || ||A occurs after B || B -> A || ||A and B occur concurrently || A | | B || ||A lasts T time || A,,T,, || ||A occurs T time after B || B ->,,T,, A || = Existential, cardinality and modal operators = We want to be able to denote how many objects or events of a given type must/may occur. ||''Meaning'' || ''Operator and example'' || ||Every object A || each A || ||Some objects A || some A || ||Some object A called a1 || some A a1 || ||A must occur || A || ||A may occur || [A] || ||Exactly N objects/events of type A || |A|,,N,, || ||At least N objects/events of type A|| |A|,,>=N,, || ||At most N objects/events of type A || |A|,,<=N,, ||