Modifiers and transforms

Modifiers

Function	Notes
`optional(schema)`	The field may be `undefined` or absent. See `optional()`
`required(schema)`	Removes `optional()`, however many times it was applied
`lazy(() => schema)`	Defers a schema until it is parsed. See `lazy()`

Each returns a new schema. Types follow the runtime change. See Composing schemas and Partial and required variants for examples.

Function	Notes
`extend(schema, shape)`	Adds or replaces fields; on a `union()` of objects, every member gets them
`omit(schema, keys)`	Removes fields. Document system fields are kept
`pick(schema, keys)`	Keeps only the listed fields (plus system fields on documents)
`rename(schema, newType)`	Replaces the `_type` literal
`shallowPartial(schema)`	Top-level fields optional
`shallowRequired(schema)`	Top-level fields required
`deepPartial(schema)`	All fields optional, recursively
`deepRequired(schema)`	All fields required, recursively