Change the machine name/title of the sidebar regions to something more semantic

Absolutely! (I thought there already was an issue for this, but I can't find it.)

• Sidebar-first -> Complementary content 1 (or simply Complementary)
• Sidebar-second -> Complementary content 2 (or simply Complementary 2)

NB: "complementary" is also an ARIA role for how these regions are typically used. However, perhaps it assumes too much and might be confusing to the more semantically minded to use the same word? So as an alternative:

• Sidebar-first -> Supplementary content 1 (or simply Supplementary)
• Sidebar-second -> Supplementary content 2 (or simply Supplementary 2)

Presentational names of regions and classes is #doingitwrong in this day and age. Let's get ride of "sidebar".

No patch attached, changing status appropriately. I agree that having "sidebar" isn't always accurate, but in spite of that I don't think we should go the opposite and put in long class names like "complementary" or "supplementary".

How about:

1. sidebar-first -> aside-first
   sidebar-second -> aside-second

- or -

2. sidebar-first -> meta-first
   sidebar-second -> meta-second

- or even more simply -

3. sidebar-first -> first (since we could just target: aside.first)
   sidebar-second -> second

I'd like to keep these names as short as possible. There's no need to add superfluous information for something that is used rather specifically anyway (ie: aside tag).

However, despite my post just now and in regards to #1649780: Remove first/last/odd/even classes in favor of CSS3 pseudo selectors, perhaps we shouldn't have even those classes (first, last). They could be targeted using pseudo selectors:

aside:nth-child(1) {}
aside:nth-child(2) {}
aside:first-of-type {}
aside:last-of-type {}

#5 sounds good for classes, but what do we call the regions themselves - so you know where you're putting your blocks in the admin UI?

Had a discussion with @dbazuin in IRC about maybe naming things based on where they appear in the markup sans-CSS (like, before or after) rather than how they appear post-CSS. The problem with that is, if you edit the template, anything could be positioned anywhere, but since this is specifically for Bartik and Stark rather than a template base theme, perhaps that isn't such an issue.

Ah, good point. "Pre-content"/"Post-content"? Considering this is just for core, I think we shouldn't worry about "if things get moved around" because we're not gonna move them. If someone decides to do that post download, then the responsibility falls onto them to update their semantic naming conventions :)

mmmm, what if someone wants to put the system content block in pre-content? what does that mean?

content_one, content_two, content_three?

Class names have dashes, not underscores :)

What about additional-first, additional-second?

Class names have dashes, not underscores

Region names have underscores. Class names are just derived from that.

I prefer before_content/after_content or pre_content/post_content as per @markcarver, as that would simultaneously be more specific and accurate.

As for additional_first/additional_second:

1. "Additional" is a relative term, what are they "in addition to"? the content? the footer? the whole page?
2. "first" and "second" don't convey information about where these regions are relative to other elements in the page, only how they sit in relation to each other.

Since these regions only exist to complement the content region, if we want their names to be semantic, they should reference both "content" and how they are positioned in the page relative to "content".

We're going around in circles now, that was already pointed out in #6 and #7, but @markcarver pointed out that we don't need to support people editing core templates to re-order regions.

The words first and second aren't really any less indicative of positioning and order than before and after IMO.

'sidebar-first' and 'sidebar-second' are constructs of Drupal's core themeing. The names mean no more than that there are 2 of them. The names are mobile friendly as they don't assert positioning, whereas words like before and after do. It is somewhat unfortunate that Drupal has embedded support for them in so much core code because people will take advantage of that support. But it imposes no obligation on themers that they be used at all or in the same way as Drupal uses them. I think the names are sufficiently semantic given their use.

#5 is going down the right road to my mind. Maybe keep classes of some form (#4, example 1 is great), that should probably work.

"sidebar" is not really a presentational class. It stems from the publishing world where a sidebar is something that holds contextually related content - which is the semantic underpinning of the "aside" element. The problem with "sidebar" is that its easily confused with "application sidebars", like a draw or panel in a desktop app, and that it uses the word "side", so we tend to think of that as being "to one side of something".

As a side note I will mention that in my D8 base theme I don't use region classes at all for layout, it's entirely done with first, last and nth-child, so I have just been through this.

So yeah, #4 + #5 looks pretty good IMO.

Just changing the title to make it clear we're actually talking about the machine name/title of the region, not whether there should be classes and what those should be named.

I think the theme can suggest how their regions are used. So calling it aside-first means the theme CSS will layout the page such that aside-first comes before aside-second. If a theme calls it pre-content-aside then it means the CSS will lay it out before the content region.

There's no right and wrong, as long as it's meaningful.