smie-forward-token-function is a variable defined in `smie.el'.
Its value is
smie-default-forward-token
This variable may be risky if used as a file-local variable.
Documentation:
Function to scan forward for the next token.
Called with no argument should return a token and move to its end.
If no token is found, return nil or the empty string.
It can return nil when bumping into a parenthesis, which lets SMIE
use syntax-tables to handle them in efficient C code.