Again following up #794936, here's my third and final bugreport for a
big clear individual issue before I start on a general proofreading
sweep.

The jargon of "low priority installs" is just plain demented.
Lowering the priority of an install would mean declaring it less
urgent, but asking for "expert mode" doesn't do that; it doesn't even
cause prompts to have a lower debconf priority (so that they're less
likely to be shown).  What it does is lower the cutoff on the
filtering-by-priority applied to debconf prompts!

Unfortunately I can't find a good single English word that conveys
this - we might perhaps say that expert mode is a "low handholdiness"
or "low automation" or "low simplification" install, but really what's
needed is for debconf to be fixed so that it works entirely the other
way around, with "debconf/prompting=high" meaning an expert-mode
install.  Alas, that's never going to happen - for a start it would
break everybody's preseeding setups.

Instead what I've gone for in my patch is the longwinded option, using
various circumlocutions based on the idea that expert mode means
having the "prompting cutoff" set to "low".  This may be hard to
follow, but that's still an improvement on having a natural and
straightforward interpretation that's completely wrong.  Constructive
alternatives gladly accepted.

In this case since I'm editing multiple files I've made this a minimal
patch, ignoring the grammar errors in neighbouring lines.

Annotated walkthrough:

A straightforward case.  As well as complicating the terminology I'm
consistently putting quotes around the names of the levels.

(Meanwhile, appendix/chroot-install.xml talks about priorities but
means something completely different by them: *package* priorities.
We really shouldn't be using the same word in two different important
technical senses at the same time!)

Another simple case.

An installation "at critical priority" would be one I'm prepared to
put a lot of effort into, not one that requires no input from me.

We can't fix this properly, but we can make it clearer.

(Meanwhile, boot-installer/parameters.xml has definitions of the boot
parameter "debconf/priority", but unless we can think of a way of
renaming that it'll have to stay as it is.)

(Then boot-installer/powerpc.xml talks about priorities but means that
in the ordinary English sense of the word.)

If I am installing "at default priority", that means it's a routine
task.  In this case that natural misinterpretation works well enough
that readers won't realise it's wrong, making them even more confused
when it falls apart later in the same file:

(Does it actually mean "e.g." there or should it be "i.e."?  Is there
anything to "expert mode" beyond the "debconf/priority=low" setting?)

This one makes me wish I could think of a replacement for the word
"cutoff" that more clearly implied the fact that the filter is a
minimum rather than a maximum level, but I can't find one.

A straightforward one.

And another.

(*I* don't need to boot!)

This has the bonus flaw of explicitly referring to the setting as the
*debconf* priority, which makes it even harder to distinguish clearly
between the debconf-priority values on the individual questions and
DI's prompt-filtering-by-debconf-priority setting.

(Besides, it's usually a mistake to refer to debconf when you don't
have to - it's meant to work invisibly behind the scenes, without
users ever needing to have their attention drawn to its presence.)

This was again focussing the spotlight on the stagehand.

(Meanwhile, using-d-i/modules/pkgsel.xml talks about priorities but
again means the other kind.)

This was a strange way of putting it, as if expert mode and "priority"
were two completely independent options.

Just futureproofing a comment.

Finally we get to the file where it actually explains things, but it
does so rather clumsily.  First we're told that all the questions are
assigned individual priorities, though we aren't told when this
happens; then we're told that the priority of some subset of questions
(the ones that are to be asked) is assigned at a particular time.  Or
no, wait, that's not it.  It means that when the installer is started,
it picks a priority level, and only asks the questions with a matching
priority.  So for instance if it picks "low", it won't ask the
high-priority questions.  No, still not right...

Instead make it clear that the second step is creating a threshold.
This isn't a complete explanation, but the rest comes later.

Add the actual explanation that was being skipped here.

I've cut a chunk out here since it seems to be badly confused.  It
claims "the question priority may be downgraded", which is backwards.
It might mean to say that a question's priority level is temporarily
*raised* or that the prompting cutoff level is temporarily *lowered*;
I would guess it's the latter, but it's hard to be sure.

My preferred solution to this mess is to throw away the unnecessary
implementation details.  The only thing that matters here is that I
won't see the menu unless something goes wrong - in which case, by
implication, I will see the menu.