This probably can't be done, but it popped into my head this morning...
When I catalog my pictures, I apply tags, so I can search for them later. I can apply multiple tags to one picture; e.g. "nature" and "baby".
It would be nice if BLF threads could have multiple tags applied to them, so that they could be categorized in more ways. Right now the lights are categorized mostly by battery type, which is fine for many people, but some people might not care about battery type and may wish that lights were categorized by physical size, or price (this is BLF after all), or LED type, etc.
A mechanism for setting the tags could be just a set of check-boxes that you can check when you first create a thread. e.g.:
□ 18650
□ AA
□ < $20 US
□ $20 < $50 US
□ > $50 US
□ pocket lights
□ toilet plunger lights
Then, in addition to the existing battery-type categories, we could have size categories and price categories. Clicking the "pocket lights" category would simply collect and display all threads that have been tagged "pocket lights". If a thread has been tagged both "pocket lights" and "AA", then clicking the "AA" category would include that thread too.
Another thing that would be nice, would be to be able to filter threads based on the tags. So if someone is interested in expensive lights but not 26650 lights, he could click the "> $50 US" category, and set the filter to exclude threads tagged "26650".