OptionallineShows line numbers next to code blocks in the preview, the viewer and the WYSIWYG editor.
The numbers aren't part of the code, so they aren't copied with it.
startFrom sets the first number (default 1); singleLine also numbers code blocks with
a single line (default false).
The highlight.js instance used for highlighting, either the full build (
import hljs from 'highlight.js') or the core with the languages you register (import hljs from 'highlight.js/lib/core').