Action item on the virtues of error-handling

One of the characteristics that distinguished the Web from preceding 
hypertext systems is that the protocols defined behavior in the 
presence of errors.  For example, HTTP defines a standard response with 
an error code (404) for a common case of a failure to access a resource 
via its URI.  Also, HTML specifies "must-ignore" processor for 
user-agents that encounter markup that is not part of HTML.  Another 
example is XML, which has a rigorous definition ("well-formedness") of 
what constitutes an XML document and how software should react when 
encountering data that fails to meet that definition.

Web Architecture requires designers of protocols and software to 
specify error-handling behavior.  There is no architectural preference 
for any particular error-handling behavior; for example both HTML's 
must-ignore policy and XML's well-formedness policy have been highly 
successful.

Cheers, Tim Bray  http://www.tbray.org/ongoing/