Like , it was saied , all you can find it's in
man file
You can see there a lot of option's ..
No the result is not a string , but I can say to you that is inspired from :
/usr/share/misc/file/magic.mime
If you want just a part of that message to be shown , you can just copy a part of it with ( STRNCPY(string,initial_string+x,y) ) from it ..