BookOnixCollectionFrequency

Explicitly unknown (u); distinct from omitting the assertion.

No fixed publication schedule (i).

Regularly scheduled, less frequently than once every two years (r).

Once every two years (e).

Once per year (a).

Twice per year (b).

Three times per year (t).

Four times per year (q).

Six times per year (s).

Once per month (m).

Once every two weeks (f).

Once per week (w).

Daily or otherwise more frequently than weekly, at least twice per week (d).

No further publications are planned in the collection (x).