Currently the substitution function supports only the following way to reference a property. "%(property)". When processed the whole string will be replaced with the value of the property. The enhancement calls to support formats like:
"%5s(property)"
"%0.5(property)"
I do not have a clear picture of what should be the syntax and what kinds of specifiers we should support. It seems that it would be logical to support things like, padding, alignment, type conversion, case conversion etc. It also makes sense to keep it close to known syntax such as of printf() function.