An arbitrary value of type t; describes an empty ghost range.
Return an empty ghost range located in a given file.
Set the file name and line number of the lexbuf to be the start
of the named file.
Get the location of the current token from the lexbuf.
rhs_loc n returns the location of the symbol at position n, starting
at 1, in the current parser rule.
In -absname mode, return the absolute path for this filename.
Otherwise, returns the filename unchanged.