However, such documents are still fully parsable in the "non"-standalone mode of validating parsers, which signals an error if it can't locate these external entities with their specified "public identifier" (FPI) or "system identifier" (a URI), or are inaccessible. (Notations declared in the DTD are also referencing external entities, but these unparsed entities are not needed for the validation of documents in the "standalone" mode of these parsers: the validation of all external entities referenced by notations is left to the application using the SGML or XML parser). Non-validating parsers "may" eventually attempt to locate these external entities in the "non"-standalone mode (by partially interpreting the DTD only to resolve their declared parsable entities), but do not validate the content model of these documents.