

Both versions of MODx can do this very easily
PHP code is handled via snippets - you have to put PHP code into a snippet and then include the snippet on the page. JS/CSS code can be inserted in a variety of ways onto a specific page - either using chunks, TVs (Template Variables) or inline in the main page content.
If some of that terminology seems strange, I suggest you take some time out to review the Evolution documentation to fully understand the concepts involved in building a MODx site.