How to change the indentation?

If you use the PRE container, tabs are preserved in the markup and handled by the browser. You can control this tab width with css (e.g. tab-size: 4;), but this is not supported by all browsers.

If you use another container, the GeSHi library replaces tabs with spaces, eight by default. It is possible to change the tab width, but this is not supported currently by the GeSHi filter for syntax highlighting module.

This is kinda simple to implement, so i will do it for drupal 8. We just need to add a new global setting: tab width and use this $geshi->set_tab_width($width); on geshiprocess.

It is working, lets see the test.

Fixed with the commit.