I18N: Mark screen reader strings as such with translator comments.

This aims to provide better context for translators and make it easier to determine that some strings contain hidden accessibility text and are not displayed in the UI.

Props kebbet, mercime, pavelevap, ocean90, swissspidy, Chouby, jipmoors, afercia, desrosj, costdev, audrasjb, SergeyBiryukov.
Fixes #29748.
Built from https://develop.svn.wordpress.org/trunk@55276


git-svn-id: http://core.svn.wordpress.org/trunk@54809 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/customize.php

@@ -207,7 +207,12 @@ do_action( 'customize_controls_head' );
 				<span class="preview"><?php _e( 'Preview' ); ?></span>
 			</button>
 			<a class="customize-controls-close" href="<?php echo esc_url( $wp_customize->get_return_url() ); ?>">
-				<span class="screen-reader-text"><?php _e( 'Close the Customizer and go back to the previous page' ); ?></span>
+				<span class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'Close the Customizer and go back to the previous page' );
+					?>
+				</span>
 			</a>
 		</div>
 
@@ -230,7 +235,12 @@ do_action( 'customize_controls_head' );
 							printf( __( 'You are customizing %s' ), '<strong class="panel-title site-title">' . get_bloginfo( 'name', 'display' ) . '</strong>' );
 						?>
 						</span>
-						<button type="button" class="customize-help-toggle dashicons dashicons-editor-help" aria-expanded="false"><span class="screen-reader-text"><?php _e( 'Help' ); ?></span></button>
+						<button type="button" class="customize-help-toggle dashicons dashicons-editor-help" aria-expanded="false"><span class="screen-reader-text">
+							<?php
+							/* translators: Hidden accessibility text. */
+							_e( 'Help' );
+							?>
+						</span></button>
 					</div>
 					<div class="customize-panel-description">
 						<p>