Clarify condition by splitting it up into explicitly named bools.

[otherdaniel]

Split the dreaded multi-line condition into several subclauses, assign each to an appropriately named boolean, and then test those bools.

That's more verbose than I usually go for, but it's surely more readable than the old version.

Fix: #380

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[evilpie]

I have been thinking it might be cleaner to add a new algorithm like is attribute allowed. This might also be useful for #387, because we could use it like "is attribute allowed is".

[otherdaniel]

I have been thinking it might be cleaner to add a new algorithm like is attribute allowed. This might also be useful for #387, because we could use it like "is attribute allowed is".

Done. Please take another look.