[wp-trac] [WordPress Trac] #64418: Valid CSS is causing failure in the Additional CSS panel

[WordPress Trac]

#64418: Valid CSS is causing failure in the Additional CSS panel
--------------------------+---------------------
 Reporter:  drw158        |       Owner:  (none)
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  7.0
Component:  Customize     |     Version:  4.7
 Severity:  normal        |  Resolution:
 Keywords:  needs-patch   |     Focuses:  css
--------------------------+---------------------

Comment (by jonsurrell):

 @sabernhardt I think this is the correct place for the ticket because this
 is Core behavior. There is some CSS validation on the frontend, but it's
 disconnected from (and often does not agree with) the logic that actually
 accepts or rejects the CSS.

 In the case of the site editor, I believe it's the global styles REST
 handler that's rejecting here, and [https://github.com/WordPress
 /wordpress-develop/blob/eda8d9d27b129ac48143af7d9c2df595dc172e44/src/wp-
 includes/rest-api/endpoints/class-wp-rest-global-styles-
 controller.php#L659-L679 it appears to have kept the same problematic
 regular expression]:

 {{{#!php
 <?php
 function validate_custom_css( $css ) {
         if ( preg_match( '#</?\w+#', $css ) ) {
                 return new WP_Error(
                         'rest_custom_css_illegal_markup',
                         __( 'Markup is not allowed in CSS.' ),
                         array( 'status' => 400 )
                 );
         }
         return true;
 }
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/64418#comment:7>
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