TagInputField.js tags xtype

CQ includes this:
http://localhost:4502/libs/cq/tagging/widgets/source/widgets/TagInputField.js

So you can configure it like this:
new CQ.tagging.TagInputField({
namespaces: ["foo", "default", "bar] //search only these namespaces
, tagsBasePath: "/content/mytags" //do NOT do this. TagManager always searches from /etc/tags anyways
, suggestMinChars: 1 //auto complete starts from one character input (default 3)
});