Stupid decision, the should have used $foo (dollar sign for variables) like in Perl and PHP. It remind me decisions of standards based on XML (XLST, XML-Schema, RDF, etc).
Read the linked post. Css variables are nothing like macros like sass's `$foo` and css might support macros with sass's `$foo` syntax in future.
I read the article, that's why I commented because "might support something in future" that probably never happens, is what I related to XML based formats design decisions go wrong. Argh, but thanks for misunderstanding and downvotings.