Changes in attribute importance starting from 6.10+

[Radek eM]

Hi Community, 

I've got a question regarding a change in attribute importance introduced in 6.10 version (which changes the order of test execution in my case) described as: 

New: Hierarchy on order features (from less important to more important): groupByInstance, preserveOrder, priority, dependsOnGroups, dependsOnMethods

I'm a little bit confused about how should I understand this order?

• in case of test cases having both - "priority" attributes in @Test and the "preserve-order=true" in XML - is the "priority" simply more important (so first, test cases are ordered by priority and then grouped by order defined in XML as preserve-order is set to true) or if there are different "priority" values in different test cases, the "priority" policy is the only one taken into considereation ignoring the preserve-order (and any other "less important" attributes?
  
• In my project (using 6.9.5) the current behavior is as follows: execute all tests from test classes according to XML and then group them by priorities - was it an expected behavior which was changed after introducing 6.10+ or a bug?
• After changing the version of TestNG (6.9.5 -> 6.10+) some of  test cases were not executed. I heard it's due to changes in attribute importance which in some cases can be non-backward-compatible and causes some conflicts between "priority" and "preserve-order". I didn't find any specific information about this (maybe it's a rare situation). Do you know about any non-backward-compatibility problems after introducing changes in attribute importance? 
  

Best regards, 

Radek