hfy-istext-command

hfy-istext-command is a variable defined in `htmlfontify.el'.
Its value is

"file %s | sed -e 's@^[^:]*:[ 	]*@@'"

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

Documentation:
Command to run with the name of a file, to see whether it is a text file
or not. The command should emit a string containing the word 'text' if
the file is a text file, and a string not containing 'text' otherwise.

You can customize this variable.