20. A non-transitory computer-readable medium encoded with instructions that, when executed by a processor, cause the processor to perform: receiving, via an active address field, a character string comprising one or more characters, repeatedly checking validity by repeatedly requesting information on the validity of said character string as a document identifier wherein the checking is implemented by the active address field receiving the character string, causing indication of a valid part of said character string comprising at least a domain part, causing indication of the validity of said character string as a whole by changing an appearance of a control element, wherein the control element is configured to cause a request for a document relating to the document identifier defined by said character string to be sent in response to selection of the control element by a user and wherein the control element does not include an indication of the document identifier defined by said character string; and causing an offering of a possibility to send a request for a document relating to the document identifier defined at least by the valid part of the character string and ignoring any other part of said character string.
21. The non-transitory computer-readable medium according to claim 20 , wherein the checking is performed by a search engine.