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However, maybe we can choose another way: use a macro like {gravatar:somebody@somewhere} . It let user do what she or he like, but user must remember put the code in snip every time.
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I think you've just hit the solution Ada! I like this option because we let the user put the avatar wherever the users wants, from comments to blog posts to snips.

I saw you edited the features including a timeline listing, isn't that what the already existing TimeLine Macro does? You can see it here: [post-history] it can display only blog posts or all snips.