If the language attribute is provided on a verbatim environment, that will be reflected in the output as a language-language class value. This is used by some browser-based syntax highlighters for language identification and can be used for styling.

When a programlisting doesn’t specify a language, the value of $verbatim-default-language will be used to construct one. No class will be output if the default language is the empty sequence. The default language only applies to programlisting elements.