Tooltips can be generated with pdfcomment package. However, they lead to some weird behavior if one clicks on a tooltiped item: the item becomes highlighted and "checked" (checked in Acrobat Reader 9 in Debian and Acrobat Reader X in Windows XP). So, it looks more like a "checkbox":

See an example below
\documentclass{article}
\usepackage{pdfcomment}
\newcommand\MyShortCut[3]{\newcommand{#1}{\pdftooltip{#2}{#3}}}
\MyShortCut{\textthing}{tooltip here}{just an example}
\MyShortCut{\Td}{\tau_\textrm{d}}{reptation time}
\MyShortCut{\Tr}{\tau_\textrm{R}}{Rouse time}
\begin{document}
Use pdflatex to compile, then open in Acrobat Reader and
put the mouse pointer above $\tau$'s
\[
\Td = 3 Z \Tr
\]
Or in text \textthing.
\end{document}
Question: is there a better way to achieve my goal: to have a tooltip when a mouse pointer is over a piece of text or a variable? Without any side effects, like the ones described above. Ideally, with hyperref only, so I do not need to load extra packages (\href does something similar).

pdfcommentexample there suffers from the same phenomenon as I have explained above. – amorua Nov 13 '11 at 19:58fancytooltipsis listed. Is this package an alternative? – Marco Daniel Nov 14 '11 at 06:15fancytooltipsis not an alternative, because of two points. First of all, it would be really an overkill for simple text-only tooltips I need. Secondly, it works only with Javascript enabled in AcroRead, whereas simple tooltips I need is a feature of PDF, which does not require Javascript (due to security reasons, it is a good idea to switch off Javascript in AcroRead, what many people, including myself, do). – amorua Nov 14 '11 at 06:48