Not sure a complex description and examples are all that useful when describing the _default_ value.
I would have thought it would be better to improve the description of the preference [in this section](https://www.geany.org/manual/current/index.html#various-preferences) (sorry there doesn't seem to be a link any closer) which is the description of the setting the user edits.
So I would add a section below the table the same as is done for Statusbar Templates, maybe `Filetype Regex`. Most of your description and examples using the default value and the importance of whatever is extracted matching the extensions file would go there with minimal changes. Then the table entry can say "See below" like Statusbar Templates does and would no longer need a link to the compile time default.