Search notes:

Documentation/

Common file types

Commonly found file types below Documentation include .txt, .rst and .yaml.
The exact number can be determined like so (executed in August 2023): 
find . -type f | awk -F/ '{split($NF, a, "."); if (length(a) > 1) print a[length(a)]; else print "<no extension>"}' | sort | uniq -c | sort -n
   … several rare filetypes omitted for brevity …
      9 sh
     15 py
     17 dot
     74 svg
    615 <no extension>
   1707 txt
   3298 rst
   3604 yaml

See also

Linux kernel sources: Documentation
Linux kernel source tree

Index