In Moodle can we search across sites?

To clarify the question, what kind of cross-site searching is available in Moodle if any? That is, within one Moodle server, is it possible to search content across multiple sites? It seems that it is possible to search the descriptions of each site, but can you do more?

Here are some use cases:

• Find all economics classes – Answer appears to be yes.
• Find all classes with a forum post by so-and-so.
• Find all classes with an uploaded file with specific words in it.
• Find all classes with Powerpoint files. Or audio or video files.

According to Mary Parke, Instructional Designer at De Anza College:

In Moodle v 1.8 there is an option that enables “global search”. It supposedly enables global text searching in resources and activities. It’s filed under “Miscellaneous”—> Experimental. It supposedly works only with PHP v. 5. I’ve enabled it in my test environment but have yet to figure out EXACTLY how it works….