Guide to LaTeX (4th Edition) (Tools and Techniques

348 Chapter 15. Presentation Material
With some tricky playing around with level numbers and with the T E X
overlap commands \rlap and \llap, it is possible to get text or images
to be replaced. The two must be made to overlap, but at different level
numbers. For example:
We now \rlap{alter}change this word
We now
\pause\pauselevel{=1 :1}\rlap{alter}\pause
change\pause\pauselevel{=1}
this word
The first line shows the text without the \pause markers, in which ‘alter’
overlaps to the right over ‘change’. The next lines show the same text with
levels inserted: ‘alter’ belongs to level 1, and disappears after 1; ‘change’
belongs to 2 (automatic increment), and the remaining text is set back to
level 1.
Highlighting instead of building
An alternative to building the page by pieces is to highlight the section of
text being discussed. In this mode, the entire page is visible, but printed
in a dull color, like gray, while the chunk of text at the current level is in
a bright color. When switching to the next view (level), that text becomes
dull, and the next chunk brightens.
To get this to work, one must inform PPower4 what the normal and
highlight colors are to be, and one must further indicate what text should
actually change. Clearly certain parts of the page are to remain as they
always are, at least the head and footlines, and possible titles. This is
done with
\pausecolors{textclr}{dullclr}{highclr}
where textclr is a dummy color that is not otherwise being used. Only text
indicated in this color will participate in the highlighting. For example
\pausecolors{cyan}{gray}{red} ...
This is the \textcolor{cyan}{text to be highlighted}
by the ...
The ‘text to be highlighted’ will normally appear in gray, but will turn
red for that view corresponding to its level number. And only for that
view! At the next view, it returns to gray. Note that the color cyan never
appears; it is only a marker for PPower4. (Well, it does appear in the first
PDF output, before post-processing.)
The highlighting mode is activated with \pausehighlight which
makes all text at all levels visible, but with this color switching feature.
The build mode can be reactivated with \pausebuild. In build mode, the