Not obvious how to search nodes along a specific axis, or multiple axes

When users don't specify an axis with their search term, MAAS ought to search every axis (i.e. tags, node name, and so on). This is handy, but wasteful and imprecise. For example, how would you be sure that "foo bar" matches exactly those nodes with tags "foo" and "bar"?

Now, it's already possible in the UI it's to search for tags, for example, using "maas-tags:foo maas-tags:bar", but this is not documented, and is overly verbose and tautological. It would be more convenient to say "tag:foo tag:bar". It would be useful to have a prefix for each axis along which we can match nodes.

Gmail search is a great example of how to do this kind of thing. It generally DTRT with free-form search terms, but if you need more precision you can use extra syntax to narrow the scope:

  from:@example.com subject:"My Aunt Tilly" is:unread

The greatness comes from the auto-completion as you're typing, so you only need to half remember what you're doing, and very rarely have to look up the syntax.

However, auto-complete is probably going to be out of scope for a long time, but the point is also that people are quite used to using foo: like prefixes to select an axis to search along. We need to display a key next to the search box for all the axes we support.