This is on a mobile site but my experience using other forums with this software says it should apply roughly to the desktop site.
If you want to search a specific forum or thread AND display the results in the logical, sensible, and easily understood 'by date' order instead of the mysterious and convoluted 'relevance' order:
After clicking the magnifying glass (or Search) and then Advanced Search, there is left-right scrolling menu that has options like:
Search everywhere
Search threads
Search members
Search media
and more
If you select 'Search threads' from that menu, you can specify a date range to limit results, posted by, sort the results by a few different methods, display the results in a couple different ways, AND select which forums you want the search to look in by checking (clicking/Ctrl-clicking) the desired forums in the drop down menu.
This is a much more clunky search function than before, of that there is absolutely no doubt, but I don't think the software allows any differently. Old search results default order was by date. 'Relevance' is not ideal. Relevant to whom?
The old search was easily contained to the forum were currently viewing by default AND the results were ideally presented. In the old search, you could widen the search if you positively wanted to by checking a box. Now you have to scroll through every single forum title in a drop down menu in 'Advanced search' to find the one you want and individually select it just to keep search from giving you results from everywhere by default.
The half-life setting will change the 'relevance factor' I guess I could call it for posts/threads. It would weight a thread/post from 2004 differently than a more recent post, for example and that would effect its placement in the search results list. But I would guess that is one factor the software uses to determine this magical relevance ordering.
All of the old search capability is there - you might make a case that the new search is more powerful - but it takes about ten times the effort and five times the clicks to do what I was able to do before in one or two (plus typing the word) and a few seconds. They made a global search function on every page. For them, it's great, as they design and implement software for many different forums across many different platforms. The search function is the same every time, on every page, on every device. And it does work. And work is exactly what it takes to get it to do what you want it to.
There are still oddities. For example, if you perform a normal search from the main page for 'Titanium' you get a list of results that look like threads.
Perform the search again but this time check 'Search titles only' and different results are listed. This is expected.
What I don't get is it seems like both lists all have 'T/titanium' in their titles. I guess I assumed that the word titanium was ubiquitous enough that there would be a lot of different threads with posts in it with that word than threads with it only in their titles. It probably has something to do with that relevance sorting and the fact we don't really know all of the default search settings in the normal search.
Here's the thing this thread:
In the spirit of other themed omnibus threads, I thought it'd be fun to have one for full titanium knives -- folders with Ti/Ti scales/handles. (There are lots of great knives out there which feature Ti, but to keep things on-theme Ti/other, Ti liners with other scales, etc. are off-topic.) I...
www.bladeforums.com
is not in the first five pages of results for either search. How exactly does the software report and order the results?
Further observation, I performed the same search while viewing the General Discussion forum. Leaving it to search 'Everywhere' seemed to provide the same global type results you would expect. Selecting 'Threads' didn't seem to alter the results. Selecting 'This Forum' finally did find the thread above. It was number 15 in the list.
Really, the relevance sorting is useless. Get rid of it or make 'by date' sorting the default for EVERY search across the board. That would clear up 90% of the (valid) gripes with search right away.