Is there a limit on how often this one can be used?
There is no limit on how frequently you can take a manual snapshot, but your most recent snapshot will overwrite the previous one.
You can mention users to notify them: @username
You can use Markdown to format your question. For more examples see the Markdown Cheatsheet.
> I’m a blockquote.
I’m a blockquote.
[I'm a link] (https://www.google.com)
I'm a link
**I am bold** I am bold
*I am italicized* I am italicized
