html
if a style tag is set inside the html
f.ex.
TD VALIGN="TOP" COLSPAN=2 style="border:0px; " /
it will interfere with html table border attributes


2
The following rule causes borders and backgrounds to be drawn around all cells:

table { empty-cells: show }

OBS!
(<)!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

(<)!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

(<)!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
this one works with 'introduction-exp', but none of the two above


look at http://www.w3schools.com
ALL about DOC TYPES