commonly available fonts (Times, Helvetica, Geneva, Courier, etc.) in your original
documents.

Clicking the "None" radio button will let the browser use its default font for all text.
Browsers typically use Times and Courier by default, although the user can change
these.

The Monospaced only option uses the HTML "Typewriter <TT>" tag to tell the browser
to use its default monospace font. When selected, all monospaced text in the original
document will be output with the Typewriter tag. Browsers typically use Courier to
display monospace text, although the user can change it (even changing it to a
proportional font).