1592 Rework rules for selecting a layout

[michaelhkay]

I've reworked the rules for selecting a layout. There's probably more to be done, but this is a start - feeback welcome. I'm marking this "revise" for the moment because I haven't finished it yet. There's no deliberate changing of the spec apart from fixing errors.

[ChristianGruen]

@michaelhkay I would need some more time to compare this with the previous approach. Do you think you could easily summarize what has mostly changed, apart from restructuring the layout selection rules?

[ChristianGruen]

What about (https://github.com/qt4cg/qtspecs/issues/1592#issuecomment-2493187896)…

Suggested change

	<p>If <code>every $e in $EE satisfies all-different($e/*/node-name())</code>
	<p>If <code>not(all-equal($EE/*/node-name()))</code>

[michaelhkay]

I don't think the replacement expression is correct.

[michaelhkay]

I think it's essentially (a) refactoring the way the layout selection rules are presented (fixing a couple of errors and omissions in the process), (b) adding notes on losslessness.

[michaelhkay]

In preference to the suggestion for defining a default layout, I have added an option disabled-layouts; for example if record layout is disabled, then an element that would have been formatted with record layout will typically be formatted with sequence layout instead. New tests needed for this option.

[ChristianGruen]

In preference to the suggestion for defining a default layout, I have added an option disabled-layouts; for example if record layout is disabled, then an element that would have been formatted with record layout will typically be formatted with sequence layout instead. New tests needed for this option.

I’m late, but wouldn't it be nicer to have an inclusive option (enable-layouts, use-layouts or just layouts) that by default includes all layouts? In practice, it might be easier to say which layout I want instead of excluding a layout and seeing if the right thing happens.

[michaelhkay]

I’m late, but wouldn't it be nicer to have an inclusive option (enable-layouts, use-layouts or just layouts) that by default includes all layouts? In practice, it might be easier to say which layout I want instead of excluding a layout and seeing if the right happens.

I think the likely scenario is that the user will start by choosing the defaults, and if there's something in the output that they don't like, they will either want to provide a specific choice for one particular element, or if it affects a number of elements, they will want to suppress that specific layout.

[ndw]

The CG agreed to merge this PR at meeting 101.