-## I certainly didn't implement it for efficiency, but thanks to our
-## search engine backend, it's typically not applied to very many
-## messages at once.
-
-## At the top level, we have a ThreadSet. A ThreadSet represents a set
-## of threads, e.g. a message folder or an inbox. Each ThreadSet
-## contains zero or more Threads. A Thread represents all the message
-## related to a particular subject. Each Thread has one or more
-## Containers. A Container is a recursive structure that holds the
-## tree structure as determined by the references: and in-reply-to:
-## headers. A Thread with multiple Containers occurs if they have the
-## same subject, but (most likely due to someone using a primitive
-## MUA) we don't have evidence from in-reply-to: or references:
-## headers, only subject: (and thus our tree is probably broken). A
-## Container holds zero or one message. In the case of no message, it
-## means we've seen a reference to the message but haven't seen the
-## message itself (yet).
+## I didn't implement it for efficiency, but thanks to our search
+## engine backend, it's typically not applied to very many messages at
+## once.
+##
+## At the top level, we have a ThreadSet, which represents a set of
+## threads, e.g. a message folder or an inbox. Each ThreadSet contains
+## zero or more Threads. A Thread represents all the message related
+## to a particular subject. Each Thread has one or more Containers. A
+## Container is a recursive structure that holds the message tree as
+## determined by the references: and in-reply-to: headers. EAch
+## Container holds zero or one messages. In the case of zero messages,
+## it means we've seen a reference to the message but haven't (yet)
+## seen the message itself.
+##
+## A Thread can have multiple top-level Containers if we decide to
+## group them together independent of tree structure, typically if
+## (e.g. due to someone using a primitive MUA) the messages have the
+## same subject but we don't have evidence from in-reply-to: or
+## references: headers. In this case Thread#each can optionally yield
+## a faked root object tying them all together into one tree
+## structure.