Wikibase introduced its own error reporting mechanism to overcome the limitations of the old error reporting system provided by MediaWiki core. Now that MW core offers better error reporting via errorformat=html and errorformat=raw, the custom format is no longer needed.

Wikibase API modules should only output our custom error format if the errorformat is not set to request the new standard error fortmat.

Note: wbparsevalue will needs custom error handling, because it reports errors separately for each input string.