I understand that an old HELP system permitted the use of tags; but, not everyone made good use of them.
In most implementations of using tags, like Blogger and YouTube, tags are freeform and an afterthought.. something you use AFTER you have done everything else. As vital as they are to building traffic, I have to admit that I sometimes don't bother.
But, in a community forum like this, we often only need a single tag because we are only (or should be) addressing a single issue. So, a DropDown like the "Post Topic In" field would be a great help at identifying the key search criteria.
If TWO DropDown boxess were used, the first might offer a list of features ("TimeLine", "Rendering", etc) and the second might offer TYPE ("Bug", "Suggestion", "Performance") as an additional qualifier.
Using DropDown boxes to select tags would be simple and quick.