Comment 7 for bug 1521518

Specification updated. <https://goo.gl/CJ1YLB> However, that is unfortunately a Canonical-only link, toolkit spec changes in general require approval from someone who is not available today, and they aren't visible to others until they are approved.

So for convenience, here's what I wrote:
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The on-screen keyboard should appear if:
* no external keyboard is connected, and a text field becomes focused; or
* an external keyboard is connected, but the most recent text typed anywhere was with the OSK, and a text field becomes focused; or
* an external keyboard is connected, and the most recent text typed was with an external keyboard, but you tap in the already-focused text field. (App developers are responsible for emulating this behavior in typable areas that are not text fields.)
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This avoids having to design a visual element for, valuable screen space being taken up by, and users having to learn, a separate control for revealing the OSK. If it doesn't appear when they want it to, they can just do what they'd probably try doing anyway, which is tapping again where they want to type.

Meanwhile, this bug report seems to have morphed from the original problem of Ubuntu believing a mouse when it claims to be a keyboard. Is there a separate bug report for that now?