Hi Jari,

"...Bill: Is there a way to include a clickable hyperlink in a tdf?"

Yes. For examples, take a look at 'gsc22.tdf', which contains
the tdf definitions for all of the click-to-download star datasets.
In several cases, 'more info' mentions the source of the data (usually
VizieR) and provides a URL. Clicking on the URL causes Guide to fire
up your browser (if it's not already running) and go to that page.
Examples are CMC-14 and 2MASS data.

In 'gsc22.tdf', you'll see how this is done: there are lines such
as

~r 3 10 ^Click here for a hyperlink//xhttp://www.projectpluto.com^\n

The above example would cause 'Click here for a hyperlink' to appear
in red within More Info. Click on that, and you'd get the Project
Pluto home page.

Some rather exotic things become possible with this. Take a look,
for example, at

http://www.projectpluto.com/gcvs2004.zip

In this case, you can click on a variable star, then on More Info,
and get a link to the AAVSO light curve (if any) for that star.

-- Bill