Standard Meta Language: are hd and tl evaluated right or left first?

Question

In Standard Meta Language, if I have a function that includes multiple successive calls to the hd and tl functions, will they be executed right to left, or left to right?

Example:

- fun secondChar s = tl hd s;
val secondChar = fn : string -> char

Will this function return the equivalent of tl ( hd s) or hd (tl s)?