I would like to change the behaviour of \alert so that the text is still red but now boldfaced, say. How can I do this? I have Googled, but all I can find is how to change the colour, as in Changing style of alert environment in beamer.
[Tex/LaTex] Changing the font for “alert” in beamer
beamerformatting
Related Solutions
Since (La)TeX doesn't have a “background color” for text, you would have to put your text inside a box which you can then color. Consider the following example using \colorbox.
\documentclass{beamer}
\setbeamercolor{alerted text}{fg=white,bg=red}
\newcommand{\boxalert}[1]{{%
\usebeamercolor{alerted text}\colorbox{bg}{\alert{#1}}%
}}
\begin{document}
\begin{frame}
Hello \boxalert{World}!
\end{frame}
\end{document}
Which renders
Edit: I'm no expert in beamer internals, so the following is nothing more than a hack. However, if you would like \boxalert to work with overlays, something like the following “seems” to work:
\newenvironment{boxalertenv}{\begin{altenv}%
{\usebeamertemplate{alerted text begin}\usebeamercolor[fg]{alerted text}\usebeamerfont{alerted text}\colorbox{bg}}
{\usebeamertemplate{alerted text end}}{\color{.}}{}}{\end{altenv}}
\newcommand<>{\boxalert}[1]{{%
\begin{boxalertenv}#2{#1}\end{boxalertenv}%
}}
...
Hello \boxalert<2>{World}!
I think that the beamer manual is probably in need of revision here. The \multiinclude macro wraps up the highlighted input using \begin{alertenv} ... \end{aletrenv} (which is how \alert is implemented). Thus the colour only applies to things which LaTeX can make coloured, i.e. where
\begingroup
\color{red}
<thing>
\endgroup
works as expected. This is not the case for PDF graphics: I suspect that Till Tantau was thinking of 'graphics' generated by Tikz when he wrote the documentation, where LaTeX can colour the material.
So the bottom line is that you'll have to colour the graphics yourself if they are generated externally.
Best Answer
After some digging, I located the definition of
\alertinbeamerbaselocalstructure.sty. The rest was easy. ;-)EDIT: There's also a more "beamer-like" way. :-)