1. A method performed by a computer program, the method comprising: receiving a first message that comprises a rule-specific error message that indicates one or more rules that were violated by a portion of an Extensible Markup Language (XML) document as a result of that portion not complying with a specified schema that is one of: (a) an XML schema and (b) a Document Type Definition (DTD); wherein the computer program does not receive, with the first message, a second message that comprises a context-specific message that sets forth the meaning of the error message in a particular implementation context; in response to receiving the first message, determining, based on a first mapping, that the first message is mapped to the second message, wherein the first mapping is not embodied in executable code; and in response to determining that the first message is mapped to the second message, outputting the second message.