filesets-open-file-function

filesets-open-file-function is a variable defined in `filesets.el'.
Its value is

filesets-find-or-display-file

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

Documentation:
The function used for opening files.

`filesets-find-or-display-file' ... Filesets' default function for
visiting files. This function checks if an external viewer is defined
for a specific file type. Either this viewer, if defined, or
`find-file' will be used to visit a file.

`filesets-find-file' ... An alternative function that always uses
`find-file'. If `filesets-be-docile-flag' is true, a file, which isn't
readable, will not be opened.

Caveat: Changes will take effect only after rebuilding the menu.

You can customize this variable.