Improve Messaging for Empty Dashboard State

[mdrovdahl]

When all columns in the wp-admin dashboard are empty (see below), the per-column messaging of "Drag boxes here" is suboptimal. In this state, there are no meta boxes to drag, but instead meta boxes must be added by going to the "Screen Options" menu.

Steps to reproduce: provision a new WP site. Go to the wp-admin dash > open Screen Options, unselect all, close Screen Options. Close your eyes, take a deep breath and pretend you don't know WP as deeply as you do, imagine someone else setup your dashboard this way. Open your eyes and try to make sense of "Drag boxes here".

Screencaps: ​https://cloudup.com/cF9DZ3koo0x

Ideas for improving this...

MVP: change the "Drag boxes here" messaging from [36295] to read "Drag boxes here, or add boxes from the Screen Options menu"

Better: detect the state where ALL columns are empty and conditionally present a different, more contextually appropriate message, eg: "Add boxes from the Screen Options menu". Maybe a change around here https://core.trac.wordpress.org/browser/trunk/src/wp-admin/js/postbox.js?rev=36295#L194 could accomplish this.

Related:

• [36295]
• #26399

CC @johnbillion and @xavortm given their prior involvement in this area.

[valentinbora]

@mdrovdahl thank you for reporting this issue and welcome to Trac.

[valentinbora]

Empty dashboard with 3 boxes, contains instructions

[valentinbora]

Empty dashboard with 4 boxes, no instructions anymore

[valentinbora]

@afercia do we need a11y to chime in on this?

[davidbaumwald]

Tagging for #accessibility review as well.

[audrasjb]

Let's start with the first proposed solution for now, to temporarily fix the issue.
Marking this as good-first-bug.

[afercia]

Related: #49288 which is going to fix more issues for the "drop areas".

[afercia]

Note: the current plan is to include a fix for this in the patch for #49288.

[afercia]

In 48340:

Accessibility: Administration: Improve the sortable postboxes areas on the Dashboard and Classic Editor pages.

• makes the postboxes areas in the Dashboard visible also on large screens
• uses a more meaningful text when all postboxes areas are empty instead of "Drag boxes here"
• restores the ability to drag boxes to the "advanced" area in the Classic Editor page
• makes the postboxes areas in the Classic Editor page visible while dragging so that users have a clue what the available areas are
• improves the color contrast of the postboxes areas while dragging
• uses wp.i18n for translatable strings in wp-admin/js/postbox.js

Props xkon, karmatosed, audrasjb, ocean90, joedolson, afercia, azaozz.
See #20491.
Fixes #49288, #47541.