Documentation: no examples for shift use

The documentation (under "Supported tags and attributes") alludes vaguely to the ability to create shiftable key labels for custom layouts but provides no syntax guidance for providing the shiftable key behaviour, and as far as I can tell all the included keyboards achieve this behaviour through using keysym rather than char.

What I want is e.g. <key char="ω" cap_char="Ω" label="ω" cap_label="Ω" id="AB05"/>

I feel that the documentation should clarify that this is impossible if it is indeed impossible.