I think the grammar for position-try-fallbacks probably wants to use <position-area> not <'position-area'>, as the latter allows none.

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More details:

The grammar for position-try-fallbacks is currently:

<'position-try-fallbacks'> = none | [ [<dashed-ident> || <try-tactic>] | <'position-area'> ]#

And the grammar for <'position-area'> is:

<'position-area'> = none | <position-area>

Combined, this means that position-try-fallbacks allows something like flip-block, none, none, none.