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SYSE.27:4.2 - Compare the change forms

Possible formWhen it can supply the needed resultBurden or limit to examine
Internal implementation changeThe consumed behavior remains within its existing promise.Show that the relevant effects are preserved, not merely that requests still parse.
Compatible extensionNew use can be added without changing supported old use.Check old defaults, limits, failure behavior and the cost of the extension.
AdapterA bounded translation can preserve the old use while a different interface operates behind it.State losses, unsupported values, extra failure points and maintenance.
Explicit versioned breakThe new result cannot honestly preserve the old promise.Name affected consumers, coexistence and the migration/recovery question.
Refusal or outside routeThe contribution is not justified or cannot be supported under the current conditions.Give an actionable reason and a legitimate alternative or missing-premise return.

A version label communicates a choice; it does not establish compatibility. Compare the actual cases and consequences before selecting the label or mechanism. Do not promise an adapter if lost information or changed physical effects would prevent the existing consumer from obtaining the promised result.