Prologue: What is an "opinion"?

 2/6's PJ Gilbert publishes this very short (6-paragraph!) opinion here, with a very interesting first paragraph:

Prologue: A Court of Appeal opinion is an explanation for a decision. In most cases the opinion should contain only the necessary facts and law to support the issue or issues to be decided. To aid the litigants, their attorneys, and the public, the opinion should be concise, readable, and filed with reasonable dispatch. Generally the opinion should not mimic law review articles. We hope to follow this model in what follows.