TypesetError.InvalidPolicy

TypesetError values are returned in Err by the typesetting operations that declare them. InvalidInput carries explanatory text for invalid measured data or boundary structure. InvalidPolicy carries explanatory text for an invalid algorithm configuration.

The string payload describes a cause. Programs distinguish failure categories by matching the variant rather than comparing library message text. Constructing an error value directly preserves its supplied string.

NoBreakOpportunities means a nonempty paragraph has no selectable penalty candidate after validation and filtering. It does not mean that the selected cost model searched unsuccessfully.

NoGreedyPlan means a validated paragraph has selectable candidates but its deterministic greedy baseline cannot reach the final unit. NoPlan means that baseline completed but the selected optimization search found no permitted complete plan.

A successful empty paragraph has two empty plans and zero candidates under the paragraph contract. It is not a missing-opportunity failure.

breakParagraph validates policy configuration before measured items. It then checks candidates, builds the greedy plan, and searches for an optimized plan in that order. The first failing stage determines the returned variant.

The policy stages check geometry, the cost model and grid combination, justification settings, and KnuthPlass settings. Item validation follows source encounter order and checks collected penalty endpoints after the measured units.

classifyBreaks applies its input and break-policy validation rules. The shared error variants do not impose paragraph validation order on break classification.

An Err contains no partial ParagraphResult and does not mutate the supplied input. Previously completed argument effects remain completed. A failure while evaluating an argument keeps its ordinary language diagnostic and prevents the typesetting call.