and try to load the font family (guessed from the font name) before trying
the local substitution.
The local(...) command expects to have a real font name and not a predefined
substitution it's why we try the font family.
Given that the `css` property isn't constant, since it contains document/font ids, we cannot just check it directly. However, we can make use of regular expressions to ensure that the format is generally correct.
