diary-nongregorian-marking-hook is a variable defined in `diary-lib.el'.
Its value is

  • This variable may be risky if used as a file-local variable.

List of functions called for marking diary file and included files.
As the files are processed for diary entries, these functions are used
to cull relevant entries. You can use any or all of
`diary-bahai-mark-entries', `diary-hebrew-mark-entries' and
`diary-islamic-mark-entries'. The documentation for these functions
describes the style of such diary entries.

You can use this hook for other functions as well, if you want them to
be run on the main diary file and any included diary files. Otherwise,
use `diary-mark-entries-hook', which runs only for the main diary file.

You can customize this variable.