This is a new feature in Tiki6 for clipping of article titles or headings to a newsletter automatically, to be emailed out.
Essentially in Tiki 6, go to admin newsletters and check the checkbox to enable clipping for the newsletter you want, and then set the type/topc you want to clip from, and the time range you want to clip.
Optionally, you can set it to "auto-clip" which transforms ~~~articleclip~~~ within the newsletter with the clip, or you can simple manually clip, i.e. cut and paste the contents of the clip (gotten by clicking Clip Now) into the contents of the newsletter.