Displaying dynamic notifications/warnings on issues

While performing various operations in JIRA, you have probably noticed popup error/warning/info messages which notify the user about the status of the operation just performed. For example, a notification message is displayed to the user as soon as an issue is created, as shown here:

How are these messages displayed? How hard is it to do something similar in a plugin?

As you might have guessed, JIRA does this with the help of built-in CSS classes or Javascript functions. AUI (Atlassian User Interface) components include messages to render such notifications on the page itself, while the AJS (Atlassian JavaScipt) framework exposes those as built-in functions.

JIRA has an interesting feature, the Announcement Banner, which can be used to make announcements to its user community via JIRA itself. The announcement banner supports HTML tags and can be used to inject JavaScript snippets into pages, if needed. This is a great incentive, given that...