Some MXR visitors try to hand craft (hack) their MXR urls. I don't have numbers (they'd be welcome) or good sets of sample urls, but I know that people expect mozilla-1.9.1 to work where the tree is actually mozilla1.9.1. The konigsberg implementation calls the file 'Error404.cgi' after the errordocument. However as case sensitivity is generally a trail of tears, the initial draft here will probably use error404.cgi. This code will be executed in two cases: 1. the user selects an invalid tree name <http://mxr.mozilla.org/mozilla-1.9.1/> 2. the user selects a valid tree with an invalid verb <http://mxr.mozilla.org/mozilla1.9.1/sources/> Generally these cases are rare, so performance doesn't need to be great. The code on konigsberg today only handles case 1.