Set a tag using Calculated Values script
// IWorkItem workItem = workingCopy.getWorkItem();
List<string style="box-sizing: border-box;"> tags = workItem.getTags2();
tags.add("NewTag");
workItem.setTags2(tags);</string>
<string style="box-sizing: border-box; font-size: 13px;">
</string>
</string>
</string>
<string style="box-sizing: border-box; font-size: 13px;">Gil</string>
Accepted answer
For all I can tell you can not set a tag using JavaScript attribute customization.
You would need to use a Java based attribute customization or a server side extension.
Note that default values are pretty much useless for your purpose, because the default value for a specific type is useless as you can change the type later and the default will not.
One other answer
The code you refer to is code for the Plain Java Client Libraries and not for the JavaScript API. This is the information for attribute customization: https://jazz.net/wiki/bin/view/Main/AttributeCustomization you basically have setValue() and that is it.
I have not tried, but the tag attributes expect a list of strings.
Comments
Sorry, I can't. Not sure how that should work. For API examples read https://jazz.net/wiki/bin/view/Main/AttributeCustomization
For some additional examples read
Last lab.
You could try to set a string as value and use a comma e.g. "tag1,tag2" or "tag1 tag2".
That is all I can do. I have no time to experiment.
https://www.google.com/search?q=java+script+set+tag+site%3Ajazz.net suggests that this might not be supported.
I doubt you can even detect a work item is moved (versus just created) in the JavaScript Attribute customization.
It might be possible to detect that in a follow up action.
My thought was to set a tag to the work-item before the move and detect it by the tag after the move. The work-item is created in the original Project Area as a child work-item and with a unique type so I wanted every such work item type to have a mark, tag in this case. Is there a way to set a default tag to a specific work-item type (e.g. task) either from script or from Default Values?