Train status <https://phabricator.wikimedia.org/T271342>

1.36.0-wmf.28 is on group0. There are some new log messages that need investigation and cleanup:

T273120 ParserOptions.php PHP Notice: Undefined index: math

T273099: Undefined class constant 'BASE_CSS_CLASS' (A fix for this one has been prepared and is expected to be deployed in about an hour).

T273101: Accessing WikiPage that cannot exist as a page: w:Help:Books/Book creator text.

Thanks to everyone for your help in moving the train along!