I often see that revision comments are formatted to be in lowercase and items are separated by a ;

edited title; deleted 41 characters in body

So my question is: what rules do I need to be aware of when leaving revision comments?

• Do they need to be in lowercase?
• How can I separate some items of my coments?
• Punctuation: do the comments need a full stop?
• Other remarkable aspects?
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Those messages are automatically generated by the system.

You can use whatever rules you want in your own edit comments, as long as they're readable; that said, if you're unsure about what style to apply, it's certainly not a bad idea to follow the example the auto-generated comments give (all lowercase, separating actions by semicolon, etc.)

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Really? I think the auto-generated comments are pretty worthless. They're the kind of thing that only a computer could generate. A human would describe the content of the edit, not how many characters they changed. "Rewrote explanation for clarity", "fixed link", "improved formatting", etc. –  Cody Gray May 18 '11 at 11:25
@Cody I mean the example they give in style, not in content. Editing to clarify –  Pëkka May 18 '11 at 11:26
@Cody Clearly, you need to read more of random's revision summaries. –  Grace Note May 19 '11 at 15:08
@Grace: Now that's what I call "style". –  Cody Gray May 19 '11 at 15:14

Consider following the example of Jeff Atwood, arguably a leader of this site:

http://meta.stackexchange.com/users/1/jeff-atwood?tab=activity&sort=revisions

Or you can go the extreme opposite, and add a comment for each and every revision:

http://meta.stackexchange.com/users/146126/grace-note?tab=activity&sort=revisions

Some enjoy adding hilarity to the revision comments that few others will ever discover (and thus will remain unoffended). Check out the examples in the revision history of this question and its many answers:

Question title that doesn't describe the problem

Song lyrics can be especially useful and enlightening, as are movie quotes:

http://meta.stackexchange.com/posts/87387/revisions

Of course, if you are keen to see what others are up to (and who isn't, really?) you may find this query useful: