Here's a little background on how searches like this work. Many of the people here are programmers and will find this boring, but if you are not among the cognoscenti, you may find this explanation helpful.
The sort order of the results of a search and the search itself are different beasts.
The search determines which groups make it into the results, the sort order determines which groups show up on top. Sophisticated search engines like Google have complex search algorithms and equally sophisticated sorting algorithms.
As far as I can see, Mark's search method is quite simple: lump together the group name, description, and tags, then look for matches against the search term. When two or more words separated by white space are in the search box, both words must appear for a match, but they can be separated by other words. If there are quotes around the search term, the term must match exactly. For example, if the search box contains [feline lymphoma] (ignore the square brackets) a description like "lymphoma is a cancer, which sometimes appears in feline pets" will be included in the results. If the box contains ["feline lymphoma"] , the previous description would not be included because extra words separate feline and lymphoma, and they appear in the wrong order.
The sort order does not affect what appears in the results, only the order the results appear. The gio group search page has four possible sort orders. These only apply when the search box is empty.
The first, and default, is Most Popular. The group with the most members appears first. The group with the next largest membership appear next, and so on.
Next is Most Active. The group with the most topics appears first.
Newest lists the most recently created group first.
By Name is a bit weird. It lists group names in ascii order, which is familiar to programmers, but strange to the uninitiated. Numbers 0-9 come first. Upper case letter A-Z next. Finally lower case letters a-z.
There is another oddity to the By Name sort. At the bottom of the page, you can select a letter. By selecting A, you get all the group names that start with A. Oddly, the names are then sorted case insensitive, i.e. case is ignored and the sort is what most people would expect of an alphabetized list.
Just thought I would lay out what is happening. I apologize for being so pedantic.