save image with mask layer to file with transparency

[bitrat]

How? Seems like something that should be straight forward.

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Answering my own question here.

mask -> active layer
right click menu -> Mask to Selection
delete mask layer
image -> active layer
fill selection with key color
colors -> color to alpha [select key color]
file -> export as png

Is there a way to do this directly, without the step using color to alpha?
It would be nice if it could all be accomplished in one step.