The difficulty is in designing a system that lends itself to intuitive
use. As suggested, the reader would normally scrawl something in
a hardcopy margin. On screen, it must be typed. Further it has to be
placed within the bounds of whatever representational system is in use.
And it must be done in a way that doesn't interfere notably with original
text. Current Web technology (HTML v2.0, cgi-bin scripts in Perl and
browsers like Netscape v1.12) doesn't properly provide for the level
of interactivity which would support an effortless notation system.
Rather, more cumbersome work-arounds are necessary, in anticipation of
Java and other environments which support true interactivity.