We could include support for previewing the syntax highlighting for a Code block by loading highlight.js into the editor, and using it to colorize the Code blocks.

In contrast to the Custom HTML block which has HTML and Preview tabs, we could have colorized text shown when the block is not selected, and then automatically colorize when de-selecting. Or perhaps the colorization should always be done when de-selected but then also provide a way to preview with tabs while it is selected.