Previewing experiments on undeployed experiment variables require checkbox

[badboy]

I followed https://experimenter.info/previewing-experiments/ to test out an experiment I had just added to my local dev build.
However I could not put the experiment into preview mode due to a schema check failure on save.
Only after asking I was pointed to the checkbox "Warn only on feature schema validation failure".

This was not obvious to me, especially because that checkbox is between 2 others and not even within the same box as where the error is pointed out (below the feature configuration textbox).
This should probably be called out in the docs.