When sorting listings on the front-end, there are two ways to treat a value as a number. First, you can edit the field settings and set it to validate as a decimal. If you need a more flexible way of setting if the field is a number, you can use this hook.
This hook can be used to change an "and" search to an "and/or" search. The hook actually works for both the quick search and advanced search settings, but in general, it was created especially for advanced searches that contain more search parameters.