Just posted 2 part series on implementing autocomplete with GAE: server-side service with Python and continuation using YUI3 AutoComplete plugin.
In particular, using autocomplete for tags similar to SO YUI3 AutoComplete plugin offers option queryDelimiter
which lets you define separator before selecting string to match. Thus, if it is set to space then plugin matches every new word typed in the textbox:
YUI().use('autocomplete', function (Y) {
Y.one('body').addClass('yui3-skin-sam');
// AutoComplete on search input field
Y.one('#search_field').plug(Y.Plugin.AutoComplete, {
queryDelimiter: ' ',
source: '/rpc.xhr?action=ac_keywords&arg0={query}'
});
});
The action ac_keywords
(defined in GAE) looks up list tags that begin with typed string.