Disclosed are arrangements which seek to update schemas in a controlled manner so that a device (3710) or service can accurately parse documents conforming to a new version of a schema (3724, 3734) without the need for translation services or extra information within the document to provide guides for translation. One embodiment provides a “best-effort” attempt to process documents of an unknown schema, based on a defined similarity threshold, instead of rejecting such documents as being invalid. The arrangements disclosed seek to provide a satisfactory output from an input document that conforms with an unexpected schema. A method for constraining evolution of a schema associated with a markup language includes the steps of defining the schema and defining a metaschema associated with the schema. The metaschema provides rules for valid changes to the schema.