PHP has a setting named display_errors that allows one to specify if various error messages should be sent to the output or not. It is recommended to keep it off, especially for the public sites, since it may reveal too much information about the application, and looks awful when seen on a public site.
However, for a developer an error report shown in time and place may prove quite valuable and usually is easier to work with then logs, etc. Of course that would mean – keep errors on in development, off in production. OK, then what we do if something weird happens in production and we want to see the errors, but we don’t want others to see them?
ASP has an interesting feature here – it allows you to display detailed error page only when accessed from local browser, but display something generic when accessed from “outside”. Maybe PHP could have some setting like display_errors=local which would enable display_errors for requests originating from developer machine but would disable it when outsider accesses it? Of course, this should be carefully done to prevent security problems, but I have a feeling it might be useful.
This can be done with an extension or even user-defined prepend script, but I think system-level mechanism might help people to use it correctly and avoid embarrassing themselves with publicly-displayed errors while keeping the stuff easy to spot for developers. Would that be useful?