The story is here
https://www.mediawiki.org/wiki/Analytics/Wikimetrics/Stories#Tag_your_own_cohort_with_existing_tags

transcript:
Story
As a WikiMetrics user, I want to manage my cohorts by selecting one or more tags from a list of standard tags.

Event occurs when user begins typing the name of a tag into the "add tag" input box on the page for one of their own cohorts. A list appears with existing tags, typing filters list to existing tag list, and selecting a suggested tag auto-completes it in the input box (like google).

Notes

Tag List: Analytics/Wikimetrics/Standard_tags
See also Analytics/Wikimetrics/Adding_New_Features/Tag_Cohorts
review-remove existing cannonical tags which may not conform to tag list above
add a link to wikipage with default tags (e.g. /analytics/wikimetrics/default_tags)
UX change

It is redundant for a user to tag a cohort with it's project (e.g. frwiki) because the default project was already specified at the cohort creation time. So rather than adding each project as a standard tag, we can update the UI to expose the default project specified at upload time.
Also, typing in a project in the search should filter the cohorts with that default project. For cohorts that have users from multiple projects (including CentralAuth cohorts), all the projects should be listed.

Version: unspecified
Severity: enhancement
Whiteboard: u=WikimetricsUser c=Wikimetrics p=5 s=2014-10-30