Standardized way of interpolating variables into PEAR_Exception messages?

Hello: While working through my PEPrs, I converted my PEAR_ErrorStack error-handling to PEAR_Exception in accordance with the RFC for error-handling in PHP 5 packages. But one thing that I seem to have lost in the conversion is the ability to interpolate variables into the messages that I pass to PEAR_Exception. I was looking for something akin to the PEAR_ErrorStack templates. Currently, it seems like every package is responsible for its own interpolation -- so a typical usage would be something like: if ($var < 0) { throw new Foo_Exception("The value of VAR cannot be '$var'."); } The problem with this approach is that it becomes very difficult to internationalize the message strings -- which is why, in my definition for File_MARC_Exception near the bottom of http://marc.coffeecode.net/highlight_MARC.php, I've defined the error codes as class constants and a static array of messages with the error codes as the keys to the array. However, I'm currently going to have to reimplement PEAR_ErrorStack's variable interpolation, or some variation on it, in my own packages. So the code will look something like: if ($var < 0) { $message = Foo_Exception::interpolateMessageVariables(Foo_Exception::$message[Foo_Exception::ERROR_VAR_BAD], $var); throw new Foo_Exception($message, Foo_Exception::ERROR_VAR_BAD); } ... but I can't be the only person facing this problem. It seems to me that it would make sense to provide a standardized solution for the problem as part of the PEAR_Exception class, and to include some examples of best practices in the package's accompanying documentation. I initially thought the ideal place to enable this would have been in the constructor (something like testing the first parameter to see if it's an array; if so, then treat the first element as the message string and any following elements as variables to be interpolated) but I can see that the constructor arguments are already overloaded. I'm open to someone telling me that I've understood PEAR_Exception all wrong, and would love to hear that there's an easy solution to the problem. Ah... and I've just been told on IRC that the RFC requiring PEAR_Exception for PHP5 packages, although "approved", is not necessarily a requirement after all. It might be nice to edit "approved...but despite that, not agreed upon or required" proposals to reflect their true status. I'm just trying to strictly follow all of the coding standards for my proposals as best I can. Dan