Hi,
I see the necessity to add some markup to the variable definition, if you use grouped activity logs.
Example:

single message:
"There is a new userpicture uploaded: !user_picture_info"

grouped message:
"There are some new userpictures uploaded: %user_picture_info%"

'group_target' => 'user_picture_info'

variable definition:
@user_picture_info=<span class="my-pic-class">[account:heartbeat-user-picture]</span> <span class="my-name-class">[account:user]</span>

Adding this markup fails at the moment.
I see something like 

"@user_picture_info=|=<span class-|-"

in the variables column of table heartbeat_activity.

Of course the markup can be included into single message, if two variables are used (!user_picture, !user_name). But this proceeding fails for aggregated messages.

The only way to resolve is to create a new token for the whole "user_picture_info".
But this is difficult,
1. if there is the need for more than one token context within the different variables,
2. if you need a markup, which includes both variables, eg. a table:

@user_picture_info=<table><tr><td class="my-pic-class">[account:heartbeat-user-picture]</td><td class="my-name-class">[account:user]</td></tr></table>