run Perl. This IFrame
*must* have the "name='perlrunner'" attribute and must be embedded at
the same level as the Perl editor IFrame(s). The frames communicate
via the "window.postMessage()" mechanism, which is safe for
cross-origin communications and sandboxing. Currently, in order to
conserve memory, a single runner serves multiple "clients", that is,
the "editor" IFrames below.

It is also possible to link to perleditor.html directly: if it
detects that it is not running in an IFrame, it will load the ru