Confusing Trigger Docs.

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.6/static/trigger-definition.html
Description:

https://www.postgresql.org/docs/devel/static/trigger-definition.html

This sentence:

"If an INSERT contains an ON CONFLICT DO UPDATE clause, it is possible that
the effects of all row-level BEFORE INSERT triggers and all row-level BEFORE
UPDATE triggers can both be applied in a way that is apparent from the final
state of the updated row, if an EXCLUDED column is referenced."

is very hard to digest.

Should "is apparent" really be "is not apparent"? If not, what does "is
apparent" mean and why is this statement here?

Then

"There need not be an EXCLUDED column reference for both sets of row-level
BEFORE triggers to execute, though."

Does this mean that both row level BEFORE INSERT and BEFORE UPDATE triggers
are always executed when ON CONFLICT DO UPDATE clause is present? Or is
there some circumstance where they are not?

If so, does this also mean that if I have a single trigger defined as BEFORE
UPDATE OR INSERT that this trigger will fire twice?