It would be useful to load content with selectors like JQuery enables people to do.
In such a way, one can load specific content from an arbitrary webpage. Maybe just using jquery selectors and .load() can do the trick.
Often is undesirable to display the entire webpage but only a portion of it.
An example of this is if you have to display something from JIRA itself, as a 3rd party plugin output, that outputs often even the JIRA menu and footer.
In this particular case, I'm using the Dependency Map plugin that displays a Map of dependencies from issues but it does it on its own page displaying also the "Jira context"; since that plugin does not provide a native JIRA gadget, I've decided to include the output in a dashboard with the Custom Content plugin, but it remains the issue of the JIRA menu and footer being displayed.