Loading and running scripts inside HTML content
Prior to 1.9, any HTML-accepting method (e.g., $(), .append(), or .wrap()) executed any scripts in the HTML and removed them from the document to prevent them from being executed again. This still broke in situations where a script might be removed and reinserted into the document using methods such as .wrap(). As of 1.9, scripts inserted into a document are executed, but left in the document and tagged as already executed so they won't be executed again even if they are removed and reinserted.
For example, external script tags included in HTML are fetched synchronously and then evaluated, which can take a significant amount of time. There is no interface to notify when or whether those scripts load, or to take corrective actions when there is an error.
Code that attempts to load a script by cloning an existing script tag and injecting that clone into the document will no longer work, because the cloned script tag has already been marked as executed. To load a new script, use jQuery.getScript() instead.