='...'" attribute directly in the IFrame
tag, for example using the "Copy Frame URL" link shown in the editor.

Note that implementing an automatic resize of the IFrame to fit its
contents is nontrivial when sandboxing is enabled, which is why a
fixed height is used below. However, see for example
http://davidjbradshaw.github.io/iframe-resizer/ - examples of how
to use this are included in the source files here.
-->

<iframe id="perl1" sandbox="allow-scripts" class="perleditor" style="height:20em;"></iframe