I never intended to show the murkiness on the word "eligible". I don't think there is need to define the word "eligible". I agree that the preferred amendment to the RRG would be to say that the Stronghold cannot be "attacked", rather than a player being unable to "declare an attack" against it. This is all not a big deal, but an RRG update would be nice.

eligible seems pretty clear. meet the defined criteria. in the absence of any specific definition (which would be on the card), the default is the rulebook itself.

at a certain point they need to assume you understand the language you're reading well enough to play at all.

in this case there's no need to clarify. "During a conflict in which you are the attacking player". There are your criteria. If the action's effect would make that illegal, then you can't do it.

If a character “cannot participate” in a conflict, that

character cannot be declared as an attacker or defender

for, move into, or be played into that conflict. If an already

participating character gains “cannot participate” status

during a conflict, move it home bowed.

It seems that you if you cannot participate, you cannot declare. but if you cannot declare, you can still participate. Any character in a conflict is said to be participating. So a Seppun Gaurdsman can never participate as an attacker against someone with imperial favor, even when charged up.