Hard 4-space tab in .md file


Code is not properly highlighted in markdown files when I indent it with by tabbing. My tab type is set to Hard and tab length to 4. However, it works when I wrap my code in \```.


Which Markdown specification do you follow? Both CommonMark and GitHub Flavored Markdown use spaces for indented code-blocks (even though the editor on the CommonMark demo page also works with tabs)