This "variables" listed above, are somehow provided by "you, i.e. myheritage". I mean, when I type "Contact webmaster link" (between <>) into the Welcome message, it shows up as a "here", giving link to webmaster's profile, or when I type "Family tree summary" (between <>), it ends up with "last update time, e.t.c " information.
I wonder if there is a list of this kind of variables provided by "you", in order to create a better Welcome message :)