like loading files and stylesheets.  A <cite>Signal</cite> object
is used to pulicise the fact that MathJax has performed certain
actions, giving other code running the the web page the chance to
react to those actions.  See <a class="reference internal" href="../synchronize.html#synchronization"><em>Synchronizing with MathJax</em></a> for more details, and <a class="reference internal" href="../signals.html#using-signals"><em>Using Signals</em></a> in particular for examples of how to specify and use
MathJ