[o11c]

It's worth noting that most of those studies are for body text. To make that more directly applicable we should exclude indentation, but the additional punctuation (especially commas, but unfortunately no parentheses) also affects it.

Shading lines can also improve readability (this is known; the rest of this comment is speculation). It's probably not enough to simply alternating between e.g. white and off-white background, unlike for tables. More likely an alternation between 3 or 4 subtly-different colors is best; maybe these can form a pattern across additional lines (e.g. 121312321). If the difference isn't subtle enough, editing will suffer whenever you break the line count, but for reference only the human eye is pretty good at aligning subtle things. Maybe even an outright paper-texture background image? (This is more often a gimmick, but it can be useful.)

[ycombobreaker]

Why exclude indentation? A block of code that is indented say... 5 levels deep at 4 spaces is missing 20 columns. If that loss of space gives the developer discomfort, it sounds like a healthy reminder about complexity. Every level of nested scope is additional mental context of "global" state for a maintainer. There should be (reasonable) pressure on the author to refactor towards less indentation/nested scope.

[andyferris]

It's an interesting point.

You can't have it both ways though - support hard line limits because the mere discomfort of long lines is insufficent to convince the programmer to refactor to something clearer, and then argue that the mere discomfort of the line limit including indentation should convince the programmer to refactor deeply nested code into something simpler. Which is it? Do we want to force limits with say a linter (80 characters of width max, 5 levels of nesting max) or let the programmer choose based on comfort?

I've had to implement things like an arbitrary-JSON formatter. Setting a fixed width including indentation doesn't work - there would always be (deeply nested) values you simply cannot print according to the rules (excluding, of course, strings which have their own difficulty). I kinda feel 80 characters excluding indentation works out ok in practice in a variety of settings.

[o11c]

Sure, excessive indentation is a code smell. But that doesn't impede the ability to read and track lines within a highly-indented block, which roughly follows the readability of prose and thus can use its numbers for comparison.