[Lucene-java Wiki] Update of "BackwardsCompatibility" by Mark Miller

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The "BackwardsCompatibility" page has been changed by Mark Miller:
http://wiki.apache.org/lucene-java/BackwardsCompatibility?action=diff&rev1=9&rev2=10

Comment:
update this a bit - closer to reality, prob still needs tweaks and additions

  
  == APIs and Compilation ==
  
- Minor versions should always have complete back-compatiblity for supported (i.e. public and protected) APIs.  That's to say, any code developed against '''X.0''' should continue to run without alteration and without recompilation (ie, simply drop in the new JAR) against all '''X.N''' releases, as long as only supported APIs are used. This is no longer the case though - back compat breaks have become more and more common over time, and you will need to refer to the "Changes in backwards compatibility policy" section of CHANGES to see all of the breaks between minor releases.
+ Minor versions should always have complete back-compatiblity for supported (i.e. public and protected). That's to say, any code developed against '''X.0''' should continue to run without alteration and without recompilation (ie, simply drop in the new JAR) against all '''X.N''' releases, as long as only supported APIs are used. Back compat breaks will be documented in the "Changes in backwards compatibility policy" section of CHANGES. For major releases, there should also be a migration guide.
  
- A major release may also introduce incompatible API changes.  The transition strategy is to introduce new APIs in release '''X.N''', deprecating old APIs, then remove all deprecated APIs in release '''X+1.0'''.
+ A major release may introduce incompatible API and runtime changes.  Within minor versions, the transition strategy is to introduce new APIs in release '''X.N''', deprecating old APIs, then remove all deprecated APIs in release '''X+1.0'''. In some cases, especially with large refactorings across major versions, there will be no deprecation path and you will need to read CHANGES and a migration guide to migrate your code.
  
- Package-private APIs (e.g. methods without any modifier such as public or protected) are not supported and thus exempt from these back-compatibility requirements. They can change without warning or intermediate deprecation.
+ Package-private APIs (e.g. methods without any modifier such as public or protected) and those marked as experimental are not supported and thus exempt from these back-compatibility requirements. They can change without warning or intermediate deprecation.
  
  == File Formats ==
  
@@ -27, +27 @@

  
  From time to time, the Lucene Developers may decide that a particular bug fix or enhancement (which does not require or involve and API change) should result in a change to the default runtime behavior in some Lucene functionality because the "new" behavior is deemed "better" or more "correct" then the existing behavior.  These changes will not necessarily be backwards compatible for some Lucene clients who may have dependencies or expectations on the "old" behavior.
  
- If a runtime behavior change is included in a release, this will be clearly noted in the CHANGES.txt file.
+ If a runtime behavior change is included in a release, this will be clearly noted in the CHANGES.txt file, along with an recommendations about handling the change in your application.
  
- If a runtime behavior change is included in Minor releases (ie: '''X.N''' to '''X.N+1''') then there will be two mechanisms available for people to "force" the old behavior:
  
+ = Contrib and Modules =
-    1. A JVM system property will be available for clients to set. (this will allow clients to force the old behavior without any code changes)
-    1. A static method will be introduced which client code can call to set some internal state prior to using any Lucene code.  (this will allow clients in environments that do not permit system properties to be set to upgrade by only adding one line of code)
- 
- = Contrib Packages =
  
  "All contribs are not created equal."
  
  The compatibility commitments of a contrib package can vary based on it's maturity and intended usage. The README.txt file for each contrib should identify it's approach to compatibility.  If the README.txt file for a contrib package does not address it's backwards compatibility commitments users should assume it does '''not''' make any compatibility commitments.
  
+ You should also consider Modules individually - a benchmark module might not make the same promises that a grouping module does.
+