DITA Processing Instructions
As DITA becomes more and more mainstream, there will be the increasing desire for DITA files to contain content and common tool functionality that is meaningful across different tools. For the common tool functionality that is best handled with processing-instructions, a standardized approach would help DITA adopters employ the most appropriate mixture of tools for the different kinds of users.
Some tools currently understand the processing-instructions used by other tools. Clearly, the need has been identified and met by some vendors. Acknowledging this need and meeting it will ultimately help tool vendors save time by designing to a single set of common functions.
Perhaps this work could be codified with syntax that provides a class-based approach, where communication around a common base class ensures some amount of interoperability, but vendors are free to derive more specific functionality using a more specialized class indicator to better leverage proprietary functionality. In a way, the suggestion is to make processing-instructions more like DITA, itself.
This page is a starting place for those interested in creating a standard DITA processing-instructions nomenclature/strategy.