Accessibility: Improve the Themes Installer navigation buttons access…

…ibility.

- really disables buttons when they look disabled (when navigation is at the first or last theme)
- when navigation is at the first or last theme, moves focus to the other navigation button, to avoid a focus loss
- improves the buttons visually hidden accessibility text

Props walbo, afercia.
Fixes #36627.

Built from https://develop.svn.wordpress.org/trunk@43020


git-svn-id: http://core.svn.wordpress.org/trunk@42849 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/theme.js

@@ -573,16 +573,26 @@ themes.view.Theme = wp.Backbone.View.extend({
 	// Handles .disabled classes for previous/next buttons in theme installer preview
 	setNavButtonsState: function() {
 		var $themeInstaller = $( '.theme-install-overlay' ),
-			current = _.isUndefined( this.current ) ? this.model : this.current;
+			current = _.isUndefined( this.current ) ? this.model : this.current,
+			previousThemeButton = $themeInstaller.find( '.previous-theme' ),
+			nextThemeButton = $themeInstaller.find( '.next-theme' );
 
 		// Disable previous at the zero position
 		if ( 0 === this.model.collection.indexOf( current ) ) {
-			$themeInstaller.find( '.previous-theme' ).addClass( 'disabled' );
+			previousThemeButton
+				.addClass( 'disabled' )
+				.prop( 'disabled', true );
+
+			nextThemeButton.focus();
 		}
 
 		// Disable next if the next model is undefined
 		if ( _.isUndefined( this.model.collection.at( this.model.collection.indexOf( current ) + 1 ) ) ) {
-			$themeInstaller.find( '.next-theme' ).addClass( 'disabled' );
+			nextThemeButton
+				.addClass( 'disabled' )
+				.prop( 'disabled', true );
+
+			previousThemeButton.focus();
 		}
 	},