I thought that there should exists ability to select entities that does not have some components/tags yet to, for example, add them; or to select entities excluding some types of them.
You just list components/tags in without filed of system definition struct when mounting them.
Currently systems queries works this way:
You pass a list of component types and/or tag types when mounting a system and these set is a match query for selection of entities which will be passed to system callback. Entity must have all components and tags defined for the system to match its query condition (but it also may have more, it hasn't to be exact match). If you need to exclude entities without some components/tags from the query result (entities mustn't have them added), you can use without condition when mount the system. If system has no specified components/tags and without conditions it is considered as a task, no queries are executed for them at each progress step, and nil is passed as first argument of callback procedure (instead of matched entities array).
