Agora specs[1] introduce expanded button semantics, but the "Buttons" visuals on p. 3 don't name or explain them.

I added that image and some explication to the existing page "Patterns and components"[2]
<mildflame on>Don't ignore existing specs just because you didn't work on them! Update pages when designs change, don't leave them to rot and mislead.</mildflame>

Because the semantics are changed, some current styles in mediawiki.ui  don't cleanly map:
*  mw-ui-primary (the main button, e.g. [Login])
 * mw-ui-constructive (an alternative, e.g. "Don't have an account?  [Join Wikipedia]" button)

The new specs distinguish continue and completion actions for the primary button, and a constructive alternative is just a plain button. mw-ui-primary can either remain the style for the complete form action (changing from blue to green!) or be a deprecated synonym for a new mw-ui-completion style, since I don't think any multi-step forms use Agora yet. I think mw-ui-constructive becomes a deprecated no-op.

Flow's CSS uses "mw-ui-button mw-ui-text" for actions that don't appear as a button (the two top rows).

[1] https://www.mediawiki.org/wiki/File:Agora_specs.pdf
[2] https://www.mediawiki.org/wiki/Wikimedia_Foundation_Design/Patterns_and_components#Buttons.2FActions

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=S Page  Features engineer