The ๐๐๐ซ๐ข๐ฉ๐ญ๐ข๐ง๐ part indicates, obviously, scripting, so we can think about what kind of scripting we know exist in Web Apps: HTML & JavaScript being the 2 most common.
Secondly, XSS is part of the INJECTION bug class (see @owasp's Top 10)