nice left lines?

[A. Villaveces]

Dag!

A small question to the context people: on some of the documentation
pdfs, there appear some nice "left margins": fat yellow lines on the
left of the text. How did you produce such nice things?

A document with these is the readme.pdf ( precisely
/.../texmf/doc/context/base/readme.pdf on tetex distros), on page 1.

Dank U!

Andres Villaveces.