Src_filter relative to?

Hi all,
noob here.
I spent a whole week trying to understand a bunch of errors this otherwise awesome tool (i.e. PlatformIO) had been throwing to my face while building multi-targeted project. Finally, I brute-forced that src_filter is NOT relative to [project_dir/src], but rather to [project_dir] itself. Once I figured that out, everything works like a charm.
Is there the mistake in the documentation, or I didn’t get it right?

Cheers,
Ivan

In Src_filter = -<src/> +<other_folder/> not taken into account the exact opposite was observed.

Are you working with the latest PlatformIO core version? (CLIpio upgrade --dev)

What’s the minimal project structure and platformio.ini to replicate your problem?