Our code analysis was primarily designed as a developer tool which allows users to see exactly which lines of code are supported in each email client. This code based report helps our users learn the ins and outs of what is supported by each client without having to guess. If you review a screenshot, it is not always obvious what to do to resolve issues.
Conflicts that are reported in our code analysis may or may not alter the final layout and in many instances, a programmer may use certain CSS properties or HTML attributes that work for a majority of email clients but not for others. There might also be other circumstances where they are forced to use code that is not supported in some clients just so that their design will render correctly in others. When certain properties or elements are not "supported" the email client in question simply ignores that code.
We also offer W3C code validation as part of our Optimizer tool. Email developers regularly use code that is not "valid" according to the W3C, so don't worry if this validation finds some issues!