I thought of another suggestion. Since there are 7 search domains, perhaps a symbol could be mapped to switch the search domain. For example, if a "-3" keyword is entered, the query could be performed on the online documentation.
I am not sure that this kind of complex search facility you also explained in your previous mail belongs to the PHP site. Most of the IDEs and browsers have the abilty to add custom URL searches or handle bookmarklets which can do this kind of things for you (select where you would like to search). Someone can also grab out JS code (mentioning the license of couse :), and make a bookmarklet out of it, so people would not even need to come to our site to have the autocompletion at their hand. If someone makes such a bookmarklet, we would be proud to host it and provide it for people to add to their browsers :)
These same people will complain if you switch to multi-keyword querying, where each keyword matches if it is contained in the entry. For them, typing a single letter will not produce their expected list, but will show all entries containing that letter, and they will be flustered. They will not want to type "^", much less learn about it. At present, the complainers will probably outweigh the rationality and you'll be forced to use the less efficient search mode. This is what has happened in my experience.
Yes, as you correctly observed, the current behaviour of the autocomplete is what people expect. If we add more features and modify the interface, people will not get the kind of autocompletion they are used to. At least this is how I see it...
Goba