For all the send and receive expressions in the "select"
statement, the channel expressions are evaluated in top-to-bottom order, along with
any expressions that appear on the right hand side of send expressions.
-A channel pointer may be <code>nil</code>,
+A channel may be <code>nil</code>,
which is equivalent to that case not
being present in the select statement
except, if a send, its expression is still evaluated.